Java中Objects类的常用方法以及从泛型列表中过滤掉空元素的方法示例

场景

使用 Java 7 引入的 java.util.Objects 类，它在流处理中相当有用。

Objects类提供了一些工具方法，都是public static修饰的。

注：

实现

1、equals(Object a, Object b)判断两个对象内容是否一样。

User user1 = new User(1,"张三",20);
        User user2 = new User(1,"张三",20);
        User user3 = new User(2,"李四",20);

        System.out.println(Objects.equals("user1","user2"));//false
        System.out.println(Objects.equals("user1","user1"));//true
        System.out.println(Objects.equals(user1,user2));//false
        System.out.println(Objects.equals(user1,user1));//true
        System.out.println(Objects.equals(user1,user3));//false
        System.out.println(Objects.equals(user1,null));//false

2、deepEquals(Object a, Object b)  验证两个数组是否深层相等（deep equality），该方法在数组比较中尤其有用。

String[] names1 = {"zhangsan","lisi"};
        String[] names2 = {"zhangsan","lisi"};
        String[] names3 = {"zhangsan","lisi","wangwu"};
        System.out.println(Objects.deepEquals(names1,names2));//true
        System.out.println(Objects.deepEquals(names1,names3));//false

3、hashCode(Object o)获取对象的哈希值，返回int值。

System.out.println(Objects.hashCode("aaa"));//96321
        System.out.println(Objects.hashCode(1));//1
        System.out.println(Objects.hashCode(user1));//717356484

4、toString(Object o)获取一个对象的字符串形式。

System.out.println(Objects.toString(1));//1
        System.out.println(Objects.toString(null));//null
        System.out.println(Objects.toString(user1));//com.ruoyi.demo.domain.User@2ac1fdc4

5、compare(T a, T b, Comparator<? super T> c)比较两个对象，返回int值。需要传入比较器。

Comparator<User> comparator1 = (u1, u2) -> {
            if (u1.getId() == u2.getId()) {
                return 1;
            } else {
                return 0;
            }
        };

        System.out.println(Objects.compare(user1,user2,comparator1));//1
        System.out.println(Objects.compare(user1,user3,comparator1));//0

6、isNull(Object obj)判断对象是否为null  nonNull(Object obj)  是否不为null

User user4 = new User(3,"赵四",20);
        User user5 = null;

        System.out.println(Objects.isNull(user4));//false
        System.out.println(Objects.isNull(user5));//true

        System.out.println(Objects.nonNull(user4));//true
        System.out.println(Objects.nonNull(user5));//false

7、requireNonNull(T obj)保证传入对象不为空，为空则抛出异常

//Objects.requireNonNull(user5);//java.lang.NullPointerException
        //Objects.requireNonNull(user5,"用户不能为空");//java.lang.NullPointerException: 用户不能为空

8、从泛型列表中过滤掉空元素

public <T> List<T> getNonNullElements(List<T> list){
        return list.stream()
                .filter(Objects::nonNull)
                .collect(Collectors.toList());
    }

方法调用

List<String> stringList = Arrays.asList("badao", null, "de", null, "chengxvyuan");
        List<String> nonNullElements = getNonNullElements(stringList);
        System.out.println(nonNullElements);//[badao, de, chengxvyuan]