Java常见八大异常（新手必看）

🌅IndexOutOfBoundsException：数组角标越界异常 角标不在数组范围内

代码演示

 

public class Test2 {
    public static void main(String[] args) {
        try {
            int[] nums = new int[5];
            System.out.println(nums[6]);
        }catch (ArrayIndexOutOfBoundsException ex){
            ex.printStackTrace();
            System.out.println(ex.getMessage());
        }
    }
}

效果如下：

🌅NullPointerException 空指针异常

代码演示

 

public class Test4 {
    private int a = 1;
    private int b = 2;
    public static void main(String[] args) {
        Test4 nullPointTest1 = new Test4();
        System.out.println(nullPointTest1.a);
        Test4 nullPointTest2 = null;
        System.out.println(nullPointTest2.b);
    }
}

效果如下：

🌅ArithmeticException 数学运算异常

代码演示

 

public class Test5 {
    public static void main(String[] args) {
        Scanner input=new Scanner(System.in);
        double shang=0;
        System.out.println("请输入第一个数：");
        int num1 = input.nextInt();
        System.out.println("请输入第二个数：");
        int num2 = input.nextInt();
        shang = num1 / num2;
        System.out.println(shang);
    }
}

当除数输入0时会发生数学运算异常
效果如下：

🌅ClassCastException 类型转换异常

代码演示

 

package 练习;
/* ClassCastException:类型转换异常
     一般在多态的向下转型中容易出现
 */
class Animal{
    public void eat() {
        System.out.println("eat");
    }
}
class Cat extends Animal{
    public void eat() {
        System.out.println("猫吃鱼");
    }
    public void play() {
        System.out.println("猫玩毛线");
    }
}
class Dog extends Animal{
    public void eat() {
        System.out.println("狗吃肉");
    }
    public void method() {
        System.out.println("狗玩球");
    }
}
public class FinalTestDemo1 {
    public static void main(String[] args) {

    <span class="hljs-type">Animal <span class="hljs-variable">a <span class="hljs-operator">= <span class="hljs-keyword">new <span class="hljs-title class_">Dog();
    <span class="hljs-type">Dog <span class="hljs-variable">d <span class="hljs-operator">= (Dog)a;
    d.eat();
    d.method();
    a = <span class="hljs-keyword">new <span class="hljs-title class_">Cat();
    <span class="hljs-type">Cat <span class="hljs-variable">c <span class="hljs-operator">= (Cat)a;
    c.eat();
    c.play();
    <span class="hljs-comment">//报错：ClassCastException:类型转换异常
    <span class="hljs-comment">//是因为上一级堆中存的是Cat的地址，而dog不能访问cat类，必须要重新创建对象
    <span class="hljs-type">Dog <span class="hljs-variable">dd <span class="hljs-operator">= (Dog)a;
}


    <span class="hljs-type">Animal <span class="hljs-variable">a <span class="hljs-operator">= <span class="hljs-keyword">new <span class="hljs-title class_">Dog();
    <span class="hljs-type">Dog <span class="hljs-variable">d <span class="hljs-operator">= (Dog)a;
    d.eat();
    d.method();
    a = <span class="hljs-keyword">new <span class="hljs-title class_">Cat();
    <span class="hljs-type">Cat <span class="hljs-variable">c <span class="hljs-operator">= (Cat)a;
    c.eat();
    c.play();
    <span class="hljs-comment">//报错：ClassCastException:类型转换异常
    <span class="hljs-comment">//是因为上一级堆中存的是Cat的地址，而dog不能访问cat类，必须要重新创建对象
    <span class="hljs-type">Dog <span class="hljs-variable">dd <span class="hljs-operator">= (Dog)a;
}
}

效果如下：

🌅NumberFormatException 数字格式化异常

代码演示

 

public class Test4{
    public static void main(String[] args) {
        String str1 = "123";
        String str2 = "12a";
        System.out.println(Integer.parseInt(str1));    //123
        System.out.println(Integer.parseInt(str2));
    }
}

效果如下：

🌅 InputMismatchException 输入不匹配异常

代码演示

 

import java.util.Scanner;
public class Test6{

public static void main(String[] args) {

Scanner input=new Scanner(System.in);

System.out.println("请输入：");

int num= input.nextInt();

}

}

效果如下：

🌅 ParseException 时间解析异常

代码演示

 

public class Test4{
    public void Test5(){
        String s="2022-01-1";
        SimpleDateFormat dtf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date datetime= null;
        try {
            datetime = dtf.parse(s);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        System.out.println(datetime);
    }
}

效果如下：

🌅StackOverFlowError 栈内存溢出异常

代码演示

 

package 练习;


public class Test8{

private int stackLength = 1;



<span class="hljs-keyword">public <span class="hljs-keyword">void <span class="hljs-title function_">stackLeak<span class="hljs-params">() {
    stackLength++;
    stackLeak();
}

<span class="hljs-keyword">public <span class="hljs-keyword">static <span class="hljs-keyword">void <span class="hljs-title function_">main<span class="hljs-params">(String[] args) <span class="hljs-keyword">throws Throwable {
    <span class="hljs-type">Test8 <span class="hljs-variable">oom <span class="hljs-operator">= <span class="hljs-keyword">new <span class="hljs-title class_">Test8();
    <span class="hljs-keyword">try {
        oom.stackLeak();
    } <span class="hljs-keyword">catch (Throwable e) {
        System.out.println(<span class="hljs-string">"stack length:" + oom.stackLength);
        <span class="hljs-keyword">throw e;
    }
}


<span class="hljs-keyword">public <span class="hljs-keyword">void <span class="hljs-title function_">stackLeak<span class="hljs-params">() {
    stackLength++;
    stackLeak();
}

<span class="hljs-keyword">public <span class="hljs-keyword">static <span class="hljs-keyword">void <span class="hljs-title function_">main<span class="hljs-params">(String[] args) <span class="hljs-keyword">throws Throwable {
    <span class="hljs-type">Test8 <span class="hljs-variable">oom <span class="hljs-operator">= <span class="hljs-keyword">new <span class="hljs-title class_">Test8();
    <span class="hljs-keyword">try {
        oom.stackLeak();
    } <span class="hljs-keyword">catch (Throwable e) {
        System.out.println(<span class="hljs-string">"stack length:" + oom.stackLength);
        <span class="hljs-keyword">throw e;
    }
}
}

效果如下：

✨最后✨

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