[记]JAVA学习01 ing
在java中,每一行代码需要在class类中运行;
每个应用从main函数开始运行;
为了运行程序,main方法必须有以下特征;
public static void main(String[ ] args)
public:所有成员可以获取;
static:有该关键字的方法可以在没有创建包含main方法的情况下运行;
void:方法不返回任何值;
例如,以下以void声明的函数没有参数且无返回值;
void test()
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在java中,每段代码以分号分割;
文档注释方法 /** 注释内容 */
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获取控制台输入
import java.util.Scanner; Scanner myVar = new Scanner(System.in);
该Scanner对象的方法,
Read a byte - nextByte()
Read a short - nextShort()
Read an int - nextInt()
Read a long - nextLong()
Read a float - nextFloat()
Read a double - nextDouble()
Read a boolean - nextBoolean()
Read a complete line - nextLine()
Read a word - next()
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获取输入并输出
import java.util.Scanner; class MyClass { public static void main(String[ ] args) { Scanner myVar = new Scanner(System.in); System.out.println(myVar.nextLine()); } }
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if语句
if (condition) { //Executes when the condition is true }
例:
public class Program { public static void main(String[] args) { int x = 7; if(x < 42) { System.out.println("Hi"); } } }
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逻辑运算符 and && , or ||
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switch语句
switch (expression) { case value1 : //Statements break; //optional case value2 : //Statements break; //optional //You can have any number of case statements. default : //Optional //Statements }
例:
public class Program { public static void main(String[] args) { int day = 3; switch(day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; case 3: System.out.println("Wednesday"); break; } } }
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while循环
like c;
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for 循环
like c;
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do while循环
like c;
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int 数组
int[ ] arr;
需定义容量以完成声明;
int[ ] arr = new int[5];
使用下标访问和修改;
arr[2] = 42;
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初始化数组
public class Program { public static void main(String[] args) { String[ ] myNames = { "A", "B", "C", "D"}; System.out.println(myNames[2]); } }
获取数组长度
public class Program { public static void main(String[] args) { int[ ] intArr = new int[5]; System.out.println(intArr.length); } }
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增强循环
遍历数组
public class Program { public static void main(String[] args) { int[ ] primes = {2, 3, 5, 7}; for (int t: primes) { System.out.println(t); } } }
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多维数组
int[ ][ ] sample = { {1, 2, 3}, {4, 5, 6} };
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Getters & Setters 保护私有变量
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构造函数:用于类初始化
public class Vehicle { private String color; Vehicle() { color = "Red"; } }
public class Vehicle { private String color; Vehicle(String c) { color = c; } }