示例：

package com.github.string.demo1;
/**
 * @author maxiaoke.com
 * @version 1.0
 */
public class Test {
    public static void main(String[] args) {
        // 字面量的定义方式
        String s1 = "123";
        String s2 = "123";
        s1 = "hello";
        System.out.println("s1 = " + s1); // s1 = hello
        System.out.println("s2 = " + s2); // s2 = 123
    }
}