java 对象、集合的非空判断

目的：使程序更严谨

***对象验证是否不为空:  if( null != obj )

***List验证不为空：if( null != list && list.size() > 0 )

***Map验证不为空：if( null != map && map.size() > 0 )

好了，废话不多说，上代码

实体类Student(随便起一个)

package com.core.test;

public class Student {

    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

测试类CollectionTest

package com.core.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class CollectionTest {
    public static void main(String[] args) {
        Student stu = new Student();
        System.out.println("student对象-->" + stu);

        List<Student> stuList = new ArrayList<Student>();
        if (null != stuList && stuList.size() > 0) {
            System.out.println("student list不为空");
        } else {
            System.out.println("student list为空");
        }
        System.out.println("student list-->" + stuList);

        // Map<String,Object> map = null;
        Map<String, Object> map = new HashMap<String, Object>();
        // map.put("stu", stu);
        if (null != map && map.size() > 0) {
            System.out.println("map 不为空");
        } else {
            System.out.println("map 为空");
        }
        System.out.println("map集合-->" + map);
    }

}

结果：

student对象-->com.core.date.Student@340d1fa5
student list为空
student list-->[]
map 为空
map集合-->{}

总结：集合判断非空除了要验证是否为null，还要验证size是否大于0

转载：https://www.cnblogs.com/xxyfhjl/p/3974486.html