java 数据类型 选择控制流程 循环控制知识点

java的基本数据类型和c语言基本一样

public class demo1 {
	public static void main(String[] args) {
		System.out.println("jianglongjiehenshuai");
		
		
		int a;
		a = 10;
		int b;
		b = 20;
		System.out.println("a = "+a);
		System.out.println("b = "+b);
		
		int c =a+b;
		
		System.out.println("c=" +c);
		
		System.out.println(a+ "+" + b + "="+ c);
	}
}

`

选择控制流程和c语言一模一样

public class demo2 {
	public static void main(String[] args) {
		int a = 100;
		
		
		if(a>= 0) {
			
			System.out.println("a是正整数");
		}else {
			System.out.println("a不是正整数");
		}
		
		
		switch(a) {
		
		case 1:System.out.println("a=1");

		case 2:System.out.println("a=2");
		
		case 3:System.out.println("a=3");
		
		case 100:System.out.println("a=100");
		}
	}
}

public class demo3 {
	public static void main(String[] args) {
		int i;
		
		for(i=0;i<20;i++) {
			
			
			System.out.println("jianglongjie henshuai!");
		}
		
		
		while(i>0) {
			
			
			System.out.println("jianglongjie henshuai!2");
			i--;
		}
		
	}
}

public class demo4 {
	public static void main(String[] args) {
		int a[] = {1,2,3};
			
		System.out.println(a[0]);
		System.out.println(a[1]);
		System.out.println(a[2]);
		
		
		// int  array[] = new int [3];  right 
		
		int array[] =null;
		
		array =new int [3];
 		
		int i;
		for(i = 0 ;i<array.length;i++) {
			array[i] = i;
		}
		for(i = 0 ;i<array.length;i++) {
			System.out.println(array[i]);
		}
	}
}