package hello;

import java.util.Scanner;

public class Hello {
    public static void main(String[] args){
        System.out.println("Hello world");
        Scanner in = new Scanner(System.in);
        System.out.println(in.nextLine());
    }
}

------------------------

package hello;

import java.util.Scanner;

public class Hello {
    public static void main(String[] args){
        System.out.println("Hello world");
        Scanner in = new Scanner(System.in);
        System.out.println("echo:"+in.nextLine());  //用"+"连接两个字符串，""里面的内容为固定输出
    }
}

package hello;

import java.util.Scanner;

public class Hello {
    public static void main(String[] args){
//        System.out.println("Hello world");
//        Scanner in = new Scanner(System.in);
//        System.out.println("echo:"+in.nextLine());
          System.out.println("2+3="+5);     //输出2+3=5用+把前面的字符串和后面的内容连接起来，则+后面的内容也变成字符串输出
    }
}

package hello;

import java.util.Scanner;

public class Hello {
    public static void main(String[] args){
//        System.out.println("Hello world");
//        Scanner in = new Scanner(System.in);
//        System.out.println("echo:"+in.nextLine());
          System.out.println("2+3="+2+3);   // 输出2+3=23
    }
}

package hello;

import java.util.Scanner;

public class Hello {
    public static void main(String[] args){
//        System.out.println("Hello world");
//        Scanner in = new Scanner(System.in);
//        System.out.println("echo:"+in.nextLine());
          System.out.println("2+3="+(2+3));  //输出2+3=5括号决定运算顺序，先计算括号里面的2+3，再做字符串连接
    }
}

package hello;

import java.util.Scanner;

public class Hello {
    public static void main(String[] args){
//        System.out.println("Hello world");
//        Scanner in = new Scanner(System.in);
//        System.out.println("echo:"+in.nextLine());
          System.out.println(2+3+"=2+3="+(2+3));  // 输出5=2+3=5，先计算最前面的2+3，在计算括号里面的2+3，再做字符串连接
    }
}