Java语法

equals与"=="的区别

equals比较的是成员变量的值是否相同，而"=="比较的是内存地址值是否相同，示例如下

每new一次就会产生新的内存空间

package test;

import org.junit.jupiter.api.Test;

public class test2 {
    @Test
    public void test() throws Exception {
        String a = new String("123");
        String b = new String("123");
        System.out.println("a==b:" + (a == b));
        System.out.println("a==b:" + a.equals(b));
        Integer c = new Integer(2);
        Integer d = new Integer(2);
        System.out.println("c==d:" + (c == d));
        System.out.println("c==d:" + c.equals(d));
    }
}

更改写法，不采用new的形式赋值则会指向同一引用地址

package test;

import org.junit.jupiter.api.Test;

public class test2 {
    @Test
    public void test() throws Exception {
        String a1 = "123";
        String b1 = "123";
        System.out.println("a1==b1:" + (a1 == b1));
        System.out.println("a1==b1:" + a1.equals(b1));
        Integer c1 = 2;
        Integer d1 = 2;
        System.out.println("c1==d1:" + (c1 == d1));
        System.out.println("c1==d1:" + c1.equals(d1));
    }
}

根据数组对象属性过滤不需要的信息

    @Test
    public void test2() throws Exception {
        @Data
        class Model {
            public String name;
            public Integer age;
        }
        List<Model> list = new ArrayList<>();
        Model model1 = new Model();
        model1.setAge(12);
        model1.setName("张三");
        Model model2 = new Model();
        model2.setAge(24);
        model2.setName("李四");
        Model model3 = new Model();
        model3.setAge(36);
        model3.setName("王五");
        Collections.addAll(list, model1, model2, model3);
        System.out.println(list);
        List<Model> result = list.stream().filter(e -> e.getAge().equals(12)).collect(Collectors.toList());
        System.out.println(result);
    }