Java基础系列：判断空指针的三种方式

空指针：针对对象类型，对象在堆中分配“房子”。空指针（null）的对象没有分配到“房子”，所以，无法使用该对象。
使用任何的对象数据时，都要进行空指针判断。
通用的方式有三种：

1. null显式判断
2. Objects.isNull(Object)隐式判断
3. CollectionUtils工具判断空指针和空数据

    @Test
    public void nullRawTest() {
        String var1 = null;
        if (null == var1) {
            logger.info(">>>>>>>>>>var1 is null");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", var1);
        }
    }

    @Test
    public void nullUnderObjectsTest() {
        String var1 = null;
        if (Objects.isNull(var1)) {
            logger.info(">>>>>>>>>>var1 is null");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", var1);
        }
    }

    @Test
    public void nullCollectionUnderRawTest() {
        List list1 = null;
        if (null == list1) {
            logger.info(">>>>>>>>>>lsit1 is null");
        } else if (list1.isEmpty()) {
            logger.info(">>>>>>>>>>list1 is empty");
        } else {
            logger.info(">>>>>>>>>>list1 is:{}", list1);
        }
    }

    
    @Test
    public void nullCollectionUnderObjectsTest() {
        List list1 = null;
        if (Objects.isNull(list1)) {
            logger.info(">>>>>>>>>>lsit1 is null");
        } else if (list1.isEmpty()) {
            logger.info(">>>>>>>>>>list1 is empty");
        } else {
            logger.info(">>>>>>>>>>list1 is:{}", list1);
        }
    }

CollectionUtils判断

Apache通用集合工具：4.4版本。

    org.apache.commons
    commons-collections4
    4.4

    @Test
    public void nullUnderCollectionUtilsTest() {
        List list1 = null;
        if (CollectionUtils.isEmpty(list1)) {
            logger.info(">>>>>>>>>>var1 is null or empty");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", list1);
        }
    }

    @Test
    public void emptyUnderCollectionUtilsTest() {
        List list1 = Collections.emptyList();
        if (CollectionUtils.isEmpty(list1)) {
            logger.info(">>>>>>>>>>var1 is null or empty");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", list1);
        }
    }

package com.monkey.java_study.functiontest;

import org.apache.commons.collections4.CollectionUtils;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.junit.Test;

import java.util.*;


public class NullPointerTest {

    private static final Logger logger = LogManager.getLogger(NullPointerTest.class);

    private static final String TEST_VALUE = "test";

    
    @Test
    public void nullRawTest() {
        String var1 = null;
        if (null == var1) {
            logger.info(">>>>>>>>>>var1 is null");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", var1);
        }
    }

    
    @Test
    public void nullUnderObjectsTest() {
        String var1 = null;
        if (Objects.isNull(var1)) {
            logger.info(">>>>>>>>>>var1 is null");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", var1);
        }
    }

    
    @Test
    public void nullCollectionUnderRawTest() {
        List list1 = null;
        if (null == list1) {
            logger.info(">>>>>>>>>>list1 is null");
        } else if (list1.isEmpty()) {
            logger.info(">>>>>>>>>>list1 is empty");
        } else {
            logger.info(">>>>>>>>>>list1 is:{}", list1);
        }
    }

    
    @Test
    public void nullCollectionUnderObjectsTest() {
        List list1 = null;
        if (Objects.isNull(list1)) {
            logger.info(">>>>>>>>>>list1 is null");
        } else if (list1.isEmpty()) {
            logger.info(">>>>>>>>>>list1 is empty");
        } else {
            logger.info(">>>>>>>>>>list1 is:{}", list1);
        }
    }

    
    @Test
    public void nullUnderCollectionUtilsTest() {
        List list1 = null;
        if (CollectionUtils.isEmpty(list1)) {
            logger.info(">>>>>>>>>>var1 is null or empty");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", list1);
        }
    }

    
    @Test
    public void emptyUnderCollectionUtilsTest() {
        List list1 = Collections.emptyList();
        if (CollectionUtils.isEmpty(list1)) {
            logger.info(">>>>>>>>>>var1 is null or empty");
        } else {
            logger.info(">>>>>>>>>>var1 is:{}", list1);
        }
    }
}