if - else 语句

public class IfYuju{
	public static void main(String[] args){
		fangF1(4);							//函数调用方式1：直接调用,out:4
		System.out.println("------------");	
		System.out.println(fangF2(3));  	//函数调用方式2：打印调用,out:3 <=3
		System.out.println("------------");	
		int number = fangF3(3);				//函数调用方式3：赋值调用
		System.out.println(++number);		//out:4
	}
	public static void fangF1(int a){		//无返回值，返回类型声明为void
		if(a > 3){							//单if语句
			System.out.println(a);
		}
	}
	public static String fangF2(int a){		//返回a，返回类型声明为String
		if(a > 3){							//if—else语句
			return a + " >3";
		}else{
			return a +" <=3";
		}
	}
	  public static int fangF3(int a){		//函数调用方式3：赋值调用，返回a，返回类型声明为int
		  if(a<3){							//if-else扩展
			  a ++;
		  }else if(a == 3){
			  a = a;
		  }else if(a > 3){
			  a --;
		  }
		  return a;
	  }
}

switch语句

public class SwitchYuju{
	public static void main(String[] args){
		int num = 3; 
		switch(num){       // ()内为表达式
			case 1:        // 检查swich后()内的返回值                        
				System.out.println("Monday");         //从上到下依次执行，
				break;                                //到符合的case开始执行语句体
			case 2:                                   //到break停止执行
				System.out.println("Tuesday");        //如果中间缺少某个break，就会发生“穿透”
				break;
			case 3:
				System.out.println("Wednesday");
				break;
			case 4:
				System.out.println("Thursday");
				break;
			case 5:
				System.out.println("Friday");
				break;
			case 6:
				System.out.println("Saturday");
				break;
			case 7:
				System.out.println("Sunday");
				break;
		}	
	}
}

for、while循环

public class ForYuju{
	public static void main(String[] args){
		for(int i = 1;i <101; i++){
			System.out.println("抄写一百遍"+ i);
		}
		System.out.println("====================");
		int i = 1;
		while(i<11){
			System.out.println("抄写十遍" + i);
			i ++;
		}
		System.out.println("====================");
		int j = 1;
		do{
			System.out.println("do-while语句最少执行一次循环体");
			j ++;
			}while(j<10);
	}
}

方法重载

public class OverLoad{
	public static void main(String[] args){
		System.out.println(sum(1, 3));        //out:4
		System.out.println(sum(2.3, 3.2));    //out:5.5
		System.out.println(sum(1,2,3));       //out:6
	}
	public static int sum(int a,int b){        
		return a + b;
	}
	public static double sum(double a, double b){    
		return a + b;
	}
	public static int sum(int a, int b, int c){
		return a + b + c;
	}
    /*
    public static double sum(int a, int b){
        return a+b;    
    } 
    错误，重载时，不能让同一输入同时被两种方法接收*/
}