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Java从入门到实战之（21）字符串之练习

1、删除字符串中的一个字符

以下实例中我们通过字符串函数 substring() 函数来删除字符串中的一个字符，我们将功能封装在 removeCharAt 函数中。

package Java_Learn.File;

public class Main {
    public static void main(String[] args) {
        String str = "this is Java";
        System.out.println(removeCharAt(str,1));
    }

    public static  String removeCharAt(String s,int pos) {
       return s.substring(0,pos)+s.substring(pos+1);
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50366:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
tis is Java

Process finished with exit code 0

2、字符串替换

使用 java String 类的 replace 方法来替换字符串中的字符：

package Java_Learn.File;

public class Main {
    public static void main(String[] args) {
        String str="Hello World";
        System.out.println(str.replace('H','W'));
        System.out.println(str.replaceFirst("He","Wa"));
        System.out.println(str.replaceAll("He","Wa"));
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50486:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
Wello World
Wallo World
Wallo World

Process finished with exit code 0

3、字符串反转

如何使用 Java 的反转函数 reverse() 将字符串反转：

package Java_Learn.File;

public class Main {
    public static void main(String[] args) {
        String str="Hello World";
       String revers=new StringBuffer(str).reverse().toString();
        System.out.println("字符串反转前:"+str);
        System.out.println("字符串反转后："+revers);
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50525:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
字符串反转前:Hello World
字符串反转后：dlroW olleH

Process finished with exit code 0

4、字符串搜索

以下实例使用了 String 类的 indexOf() 方法在字符串中查找子字符串出现的位置，如果存在返回字符串出现的位置（第一位为0），如果不存在返回 -1：

package Java_Learn.File;

public class Main {
    public static void main(String[] args) {
        String str="Hello World";
        int index=str.indexOf("Hello");
        if(index==-1)
        {
            System.out.println("没有找到字符串Hello");
        }
        else
        {
            System.out.println("Hello字符串位置是："+index);
        }
        find(str,"World");
    }
    public static void find(String sou,String obj)
    {
        int index=sou.indexOf(obj);
        if (index==-1)
        {
            System.out.println("没有找到字符串"+obj);
        }
        else
        {
            System.out.println(obj+"字符串位置是："+index);
        }
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50676:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
Hello字符串位置是：0
World字符串位置是：6

Process finished with exit code 0

5、字符串分割

使用了 split(string) 方法通过指定分隔符将字符串分割为数组：

package Java_Learn.File;

public class Main {
    public static void main(String[] args) {
        String str = "www-runoob-com";
        spitStr(str,"-");
    }
    public static void spitStr(String str,String delimeter)
    {
        String [] tmp1;
        tmp1=str.split(delimeter);
        for(String x:tmp1)
        {
            System.out.print(x+" ");
        }
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50848:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
www runoob com 
Process finished with exit code 0

6、字符串分隔(StringTokenizer)

使用 StringTokennizer 设置不同分隔符来分隔字符串，默认的分隔符是：空格、制表符（\t）、换行符(\n）、回车符（\r）。

package Java_Learn.File;

import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        String str = "www-runoob-com";
        spitStr(str,"-");
    }
    public static void spitStr(String str,String delimeter) {
        StringTokenizer stringTokenizer=new StringTokenizer(str,delimeter);
        while (stringTokenizer.hasMoreElements())
        {
            System.out.print(stringTokenizer.nextElement()+" ");
        }
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50932:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
www runoob com

7、字符串大小写转换

package Java_Learn.File;

import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        String str = "www-runoob-com";
        toUpper(str);
        toLower(str);
    }
//    转大写
    public static void toUpper(String str) {
        System.out.println(str.toUpperCase());
    }
//    转小写
    public static void toLower(String string)
    {
        System.out.println(string.toLowerCase());
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=50998:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
WWW-RUNOOB-COM
www-runoob-com

Process finished with exit code 0

8、两个字符串区域是否相等

first_str.regionMatches(11, second_str, 12, 9) 表示将 first_str 字符串从第11个字符"M"开始和 second_str 字符串的第12个字符"M"开始逐个比较，共比较 9 对字符，由于字符串区分大小写，所以结果为false。

如果设置第一个参数为 true ，则表示忽略大小写区别，所以返回 true。

package Java_Learn.File;

import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        String first_str = "Welcome to Microsoft";
        String second_str = "I work with microsoft";
        System.out.println("区分大小写返回值"+str_Eqeal(false,first_str,second_str,12,9,11));
        System.out.println("不区分大小写返回值"+str_Eqeal(true,first_str,second_str,12,9,11));
    }
    public static boolean str_Eqeal(boolean flag,String str1,String str2,int start,int end,int index)
    {
        boolean b1=str1.regionMatches(flag,index,str2,start,end);
        return b1;
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=51154:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
区分大小写返回值false
不区分大小写返回值true

Process finished with exit code 0

9、字符串性能比较测试

通过两种方式创建字符串，并测试其性能

package Java_Learn.File;

import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args){
        long startTime = System.currentTimeMillis();
        for(int i=0;i<50000;i++){
            String s1 = "hello";
            String s2 = "hello";
        }
        long endTime = System.currentTimeMillis();
        System.out.println("通过 String 关键词创建字符串"
                + " : "+ (endTime - startTime)
                + " 毫秒" );
        long startTime1 = System.currentTimeMillis();
        for(int i=0;i<50000;i++){
            String s3 = new String("hello");
            String s4 = new String("hello");
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println("通过 String 对象创建字符串"
                + " : " + (endTime1 - startTime1)
                + " 毫秒");
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=51200:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
通过 String 关键词创建字符串 : 8 毫秒
通过 String 对象创建字符串 : 12 毫秒

Process finished with exit code 0

10、字符串优化

通过 String.intern() 方法来优化字符串：

package Java_Learn.File;

import java.util.StringTokenizer;

public class Main {
        public static void main(String[] args){
            String variables[] = new String[50000];
            for( int i=0;i <50000;i++){
                variables[i] = "s"+i;
            }
            long startTime0 = System.currentTimeMillis();
            for(int i=0;i<50000;i++){
                variables[i] = "hello";
            }
            long endTime0 = System.currentTimeMillis();
            System.out.println("直接使用字符串： "+ (endTime0 - startTime0)  + " ms" );
            long startTime1 = System.currentTimeMillis();
            for(int i=0;i<50000;i++){
                variables[i] = new String("hello");
            }
            long endTime1 = System.currentTimeMillis();
            System.out.println("使用 new 关键字：" + (endTime1 - startTime1) + " ms");
            long startTime2 = System.currentTimeMillis();
            for(int i=0;i<50000;i++){
                variables[i] = new String("hello");
                variables[i] = variables[i].intern();
            }
            long endTime2 = System.currentTimeMillis();
            System.out.println("使用字符串对象的 intern() 方法: "
                    + (endTime2 - startTime2)
                    + " ms");
        }
    }

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=51262:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
直接使用字符串： 7 ms
使用 new 关键字：3 ms
使用字符串对象的 intern() 方法: 27 ms

Process finished with exit code 0

11、字符串格式化

通过 format() 方法来格式化字符串，还可以指定地区来格式化：

package Java_Learn.File;

import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        double e = Math.E;
        System.out.format("%f%n",e);
        System.out.format(Locale.CANADA,"%-10.4f%n%n", e);
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=51306:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
2.718282
2.7183    


Process finished with exit code 0

12、连接字符串

通过 "+" 操作符和StringBuffer.append() 方法来连接字符串，并比较其性能：

package Java_Learn.File;
public class Main {
    public static void main(String[] args) {
        long startTime = System.currentTimeMillis();
        for(int i=0;i<5000;i++){
            String result = "This is"
                    + "testing the"
                    + "difference"+ "between"
                    + "String"+ "and"+ "StringBuffer";
        }
        long endTime = System.currentTimeMillis();
        System.out.println("字符串连接"
                + " - 使用 + 操作符 : "
                + (endTime - startTime)+ " ms");
        long startTime1 = System.currentTimeMillis();
        for(int i=0;i<5000;i++){
            StringBuffer result = new StringBuffer();
            result.append("This is");
            result.append("testing the");
            result.append("difference");
            result.append("between");
            result.append("String");
            result.append("and");
            result.append("StringBuffer");
        }
        long endTime1 = System.currentTimeMillis();
        System.out.println("字符串连接"
                + " - 使用 StringBuffer : "
                + (endTime1 - startTime1)+ " ms");
    }
}

结果：

"C:\Program Files\Java\jdk1.8.0_221\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=51349:C:\Program Files\JetBrains\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_221\jre\lib\rt.jar;C:\app\WorkSpace\target\classes;C:\Program Files (x86)\scala\lib\scala-actors-2.11.0.jar;C:\Program Files (x86)\scala\lib\scala-actors-migration_2.11-1.1.0.jar;C:\Program Files (x86)\scala\lib\scala-library.jar;C:\Program Files (x86)\scala\lib\scala-parser-combinators_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-reflect.jar;C:\Program Files (x86)\scala\lib\scala-swing_2.11-1.0.1.jar;C:\Program Files (x86)\scala\lib\scala-xml_2.11-1.0.1.jar;C:\repository\org\scala-lang\scala-library\2.11.0\scala-library-2.11.0.jar" Java_Learn.File.Main
字符串连接 - 使用 + 操作符 : 1 ms
字符串连接 - 使用 StringBuffer : 28 ms

Process finished with exit code 0

 

 posted on 2020-10-22 11:01  大码王  阅读(159)  评论(0)  编辑  收藏  举报
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