* 1.判断定义为String类型的s1和s2是否相等
* String s1 = "abc";
* String s2 = "abc";
* System.out.println(s1 == s2);
* System.out.println(s1.equals(s2));
* 2.下面这句话在内存中创建了几个对象?
* String s1 = new String("abc");
* 3.判断定义为String类型的s1和s2是否相等
* String s1 = new String("abc");
* String s2 = "abc";
* System.out.println(s1 == s2);
* System.out.println(s1.equals(s2));
* 4.判断定义为String类型的s1和s2是否相等
* String s1 = "a" + "b" + "c";
* String s2 = "abc";
* System.out.println(s1 == s2);
* System.out.println(s1.equals(s2));
* 5.判断定义为String类型的s1和s2是否相等
* String s1 = "ab";
* String s2 = "abc";
* String s3 = s1 + "c";
* System.out.println(s3 == s2);
* System.out.println(s3.equals(s2));
案例:- package com.itheima.string;
- public class Demo_String {
- public static void main(String[] args) {
- //demo1();
- //demo2();
- //demo3();
- //demo4();
- demo5();
- }
- private static void demo5() {
- String s1 = "ab";
- String s2 = "abc";
- String s3 = s1 + "c";
- System.out.println(s3 == s2);
- System.out.println(s3.equals(s2)); //true
- }
- private static void demo4() {
- //byte b = 3 + 4; //在编译时就变成7,把7赋值给b,常量优化机制
- String s1 = "a" + "b" + "c";//java中有常量优化机制,在编译时期就能确定s2的值为"abc",所以编译时期,在常量池中创建"abc"
- String s2 = "abc";//执行到这里时常量池中已经有了"abc",所以就不再创建,所以s1和s2指向的是常量池中同一个字符串常量"abc"
- System.out.println(s1 == s2); //true,java中有常量优化机制
- System.out.println(s1.equals(s2)); //true
- }
- private static void demo3() {//==比较的是地址值
- String s1 = new String("abc"); //录的是堆内存对象的地址值
- String s2 = "abc"; //记录的是常量池中的地址值
- System.out.println(s1 == s2); //false
- System.out.println(s1.equals(s2)); //true
- }
- private static void demo2() {
- //创建几个对象
- //创建两个对象,一个在常量池中,一个在堆内存中
- String s1 = new String("abc");
- System.out.println(s1);
- }
- private static void demo1() { //常量池中没有这个字符串对象,就创建一个,如果有直接用即可
- String s1 = "abc";
- String s2 = "abc";
- System.out.println(s1 == s2); //==号比较的是地址值,true
- System.out.println(s1.equals(s2)); //比较的是字符串的内容:true
- }
- }
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