java语法记录

字符操作

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;

public class hello3 {
    public static void main(String[] args) {
        String str="To be or not to be is a question";
        String ss[]=str.split(" ");
        Arrays.sort(ss,(String o1,String o2)->o1.length()-o2.length());
        Arrays.sort(ss, Comparator.comparingInt(String::length));
        System.out.println(Arrays.toString(ss));
        String s=String.join("\n",ss);
        System.out.println(s);
        ArrayList names=new ArrayList();
        names.add("1"); names.add("2"); names.add("3");
        System.out.println(String.join("-", names));


    }

}

二维各种数组比较

import java.util.Arrays;

public class hello3 {
    public static void main(String[] args) {
        String s1="abc";
        String s2="abc";
        String s3=new String("ab");
        System.out.println(s3.compareTo(s1));

        Object[][] a={{20,"male"},{21,"female"},{20,"female"},{19,"male"},{20,"male"}};
        Arrays.sort(a,(Object[] o1,Object o2[])->(int)o1[0]==(int)o2[0]?
                ((String)o1[1]).compareTo((String)o2[1]):(int)o1[0]-(int)o2[0]);
        System.out.println(Arrays.deepToString(a));
    }
}

StringBuffer

public class hello3 {

    public static void main(String[] args) {
        StringBuffer s1=new StringBuffer("");
        String s2=s1.toString();

        int n=8,m=3,k=0;
        for(int i=0;i<n;i++)s1.append((char)('A'+i));
        System.out.println(s1);
        while(s1.length()>1){
            k=(k+m-1)%s1.length();
            s1.deleteCharAt(k);
        }
        System.out.println(s1);
        System.out.println(s1.charAt(0)-'A'+1);


    }

}

//string valueOf
public class Test {
public static void main(String args[]) {
double d = 1100.00;
boolean b = true;
long l = 1234567890;
char[] arr = {'r', 'u', 'n', 'o', 'o', 'b' };

    System.out.println("返回值 : " + String.valueOf(d) );
    System.out.println("返回值 : " + String.valueOf(b) );
    System.out.println("返回值 : " + String.valueOf(l) );
    System.out.println("返回值 : " + String.valueOf(arr) );
}

}

//
import java.util.HashMap;
public class J84 {
    public static void main(String[] args) {
        HashMap hp=new HashMap();
        String s="Jinan University";
        char ch;int i;
        for(i=0;i<s.length();i++){
            ch=s.charAt(i);
            if(('a'<=ch)&&(ch<='z'))
                hp.put((char)(ch-32), (int)hp.getOrDefault((char)(ch-32), 0)+1);;
            if(('A'<=ch)&&(ch<='Z'))
                hp.put(ch, (int)hp.getOrDefault(ch, 0)+1);
        }
        System.out.println(hp);
    }
}