String的使用

import org.junit.Test;


public class StringTest {
    
    @Test
    public void test4(){
        String s1 = "javaEEhadoop";
        String s2 = "javaEE";
        String s3 = s2 + "hadoop";
        System.out.println(s1 == s3);//false

        final String s4 = "javaEE";//s4:常量
        String s5 = s4 + "hadoop";
        System.out.println(s1 == s5);//true
    }

    @Test
    public void test3(){
        String s1 = "javaEE";
        String s2 = "hadoop";

        String s3 = "javaEEhadoop";
        String s4 = "javaEE" + "hadoop";
        String s5 = s1 + "hadoop";
        String s6 = "javaEE" + s2;
        String s7 = s1 + s2;

        System.out.println(s3 == s4);//true
        System.out.println(s3 == s5);//false
        System.out.println(s3 == s6);//false
        System.out.println(s3 == s7);//false
        System.out.println(s5 == s6);//false
        System.out.println(s5 == s7);//false
        System.out.println(s6 == s7);//false

        String s8 = s5.intern();//返回值得到的s8使用的常量池中已经存在的"javaEEhadoop"
        System.out.println(s3 == s8);//true
    }


    

    @Test
    public void test2(){
        //通过字面量定义的方式：此时的s1和s2的数据javaEE声明在方法区中的字符串常量池中。
        String s1 = "javaEE";
        String s2 = "javaEE";
        //通过new + 构造器的方式：此时的s3和s4保存的地址值，是数据在堆空间中开辟以后对应的地址值
        String s3 = new String("javaEE");
        String s4 = new String("javaEE");

        System.out.println(s1 == s2);//true
        System.out.println(s1 == s3);//false
        System.out.println(s1 == s4);//false
        System.out.println(s3 == s4);//false

        System.out.println("***************");
        Person p1 = new Person("Tom", 12);
        Person p2 = new Person("Tom", 12);

        System.out.println(p1.name.equals(p2.name));//true
        System.out.println(p1.name == p2.name);//true


        p1.name = "Jerry";
        System.out.println(p2.name);//Tom
    }

    

    @Test
    public void test1(){
        String s1 = "abc";//字面量的定义方式
        String s2 = "abc";
//        s1 = "hello";

        System.out.println(s1 == s2);//比较s1和s2的地址值

        System.out.println(s1);
        System.out.println(s2);

        System.out.println("*******************");

        String s3 = "abc";
        s3 += "def";
        System.out.println(s3);//abcdef
        System.out.println(s2);//abc

        System.out.println("*******************");
        String s4 = "abc";
        String s5 = s4.replace('a', 'm');
        System.out.println(s4);//abc
        System.out.println(s5);//mbc
    }
}