java空指针异常如何解决

Java空指针异常(NullPointerException)是Java编程中常见的一种运行时异常，当程序试图访问一个未初始化的对象引用时，就会抛出这个异常，空指针异常的产生原因有很多，例如变量未初始化、方法返回值为null等，本文将详细介绍如何解决Java空指针异常问题，并在最后提出四个相关问题及解答。

空指针异常的原因及示例

1、变量未初始化

public class Test {
    public static void main(String[] args) {
        String str = null;
        System.out.println(str.length());
    }
}

2、方法返回值为null

public class Test {
    public static String getName() {
        return null;
    }
    public static void main(String[] args) {
        String name = getName();
        System.out.println(name);
    }
}

3、数组越界

public class Test {
    public static void main(String[] args) {
        int[] arr = new int[5];
        System.out.println(arr[5]);
    }
}

解决空指针异常的方法及技巧

1、使用if语句进行非空判断

if (str != null) {
    System.out.println(str.length());
} else {
    System.out.println("字符串为空");
}

2、使用Objects类的requireNonNull方法进行非空判断(Java 8及以上版本)

import java.util.Objects;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Supplier;
import java.util.function.UnaryOperator;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import javax.annotation.Nullable;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.TreeMap;
import java.util.Iterator;
import java.util.NoSuchElementException;
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