字符串和最终字符串之间的区别

Question

public class ExampleString {
    public static void main(String[] args) {
        String s1="u cannot change me!";
        String s2="u cannot change me!";
        String s3="u cannot"+" change me!";
        String s4="u cannot";
        String s5=s4+" change me!";
        final String s6="u cannot";
        String s7=s6+" change me!";

        System.out.println("s1==s2 "+(s1==s2));//true
        System.out.println("s1==s3 "+(s1==s3));//true
        System.out.println("s1==s5 "+(s1==s5));//false  why  it is false
        System.out.println("s1==s7 "+(s1==s7));//true   why  it is true
        System.out.println("s4==s6 "+(s4==s6));//true 
      //  System.out.println("s5 "+s5);
       // System.out.println("s7 "+s7);
        System.out.println("s5==s7 "+(s5==s7));//false  why                     
    }
}

如果是s5进行连接，但它会给出输出错误 在s7的情况下也在进行连接，它会给出真实的。 我声明s6 am声明字符串作为最终字符串变得正确 我的问题是它为什么这样给予或者它们之间有什么区别