异常（Exception）

捕获异常

public class test {
    public static void main(String [] args) {
    	int[] arr= {
    			1,2,3,4,5
    	};
    	try {
    		System.out.println(arr[10]);
    	}catch (ArrayIndexOutOfBoundsException e) {//索引越界异常
			System.out.println("索引越界");
		}
    	System.out.println("看看我是否执行");
    }
}

异常的常见方法

1.getMessage()

public class test {
    public static void main(String [] args) {
    	int[] arr= {
    			1,2,3,4,5
    	};
    	try {
    		System.out.println(arr[10]);
    	}catch (ArrayIndexOutOfBoundsException e) {//索引越界异常
    	    String message=e.getMessage();
			System.out.println(message);
		}
    	System.out.println("看看我是否执行");
    }
}

2.toString()

public class test {
    public static void main(String [] args) {
    	int[] arr= {
    			1,2,3,4,5
    	};
    	try {
    		System.out.println(arr[10]);
    	}catch (ArrayIndexOutOfBoundsException e) {//索引越界异常
    	    String str=e.toString();
			System.out.println(str);
		}
    	System.out.println("看看我是否执行");
    }
}

3.printStackTrace()

public class test {
    public static void main(String [] args) {
    	int[] arr= {
    			1,2,3,4,5
    	};
    	try {
    		System.out.println(arr[10]);
    	}catch (ArrayIndexOutOfBoundsException e) {//索引越界异常
    	   e.printStackTrace();
		}
    	System.out.println("看看我是否执行");
    }
}

抛出异常

throw:

public class test {
    public static void main(String [] args) {
    	int[] arr= null;
    	int max=getmax(arr);
    	System.out.println(max);
    }
    public static int getmax(int [] arr) {
    	if(arr==null) {
    		throw new NullPointerException();//此方法结束，下面代码不会执行
    	}
    	System.out.println("看看我执行了没");
    	int max=arr[0];
    	for(int i=0;i<arr.length;i++) {
    		if(max<arr[i]) {
    			max=arr[i];
    		}
    	}
    	return max;
    }
}

throws:

public class test {
    public static void main(String [] args) {
    	int[] arr= null;
    	int max=0;
    	try {
    	 max=getmax(arr);
    	}catch (NullPointerException e) {
    		System.out.println("空指针异常");
		}
    	
    	System.out.println(max);
    }
    public static int getmax(int [] arr)throws NullPointerException {
    	if(arr==null) {
    		throw new NullPointerException();//此方法结束，下面代码不会执行
    	}
    	System.out.println("看看我执行了没");
    	int max=arr[0];
    	for(int i=0;i<arr.length;i++) {
    		if(max<arr[i]) {
    			max=arr[i];
    		}
    	}
    	return max;
    }
}

综合练习

键盘录入数据需求:键盘录入自己心仪的女朋友姓名和年龄。姓名的长度在3~10之间，年龄的范围为18- 40岁，超出这个范围是异常数据不能赋值，需要重新录入,一直录到正确为止。

package test02;

import javax.management.RuntimeErrorException;

public class Girl {

	private String name;
	private int age;
	public Girl() {
		
	}
	public Girl(String name,int age) {
		this.setName(name);
		this.setAge(age);
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		int len=name.length();
		if(len<3||len>10) {
			throw new RuntimeException();
		}
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		if(age<18||age>40) {
			throw new RuntimeException();
		}
		this.age = age;
	}
	@Override
	public String toString() {
		return "Girl [name=" + name + ", age=" + age + "]";
	}
	
}

public class test {
    public static void main(String [] args) {
    	Scanner sc=new Scanner(System.in);
    	Girl girl=new Girl();//创建对象
    	while(true) {
    	try {
    	System.out.println("请输入姓名：");
        String name=sc.next();
        girl.setName(name);
        //年龄
        System.out.println("请输入年龄：");
        int age=sc.nextInt();
        girl.setAge(age);
        break;
    	} catch (RuntimeException e) {
			System.out.println("姓名或年龄范围有误");
		}
    }
    	System.out.println(girl);
    }
}

自定义异常

1）定义异常类

2）写继承关系

3）空参构造

4）带参构造

package test02;
public class NameFormatException extends RuntimeException{
	public  NameFormatException() {		
	}
  public  NameFormatException(String message) {
		super(message);
	}
}

package test02;
public class AgeBoundException extends RuntimeException {
	public AgeBoundException() {	
	}
public AgeBoundException(String message) {
		super(message);
	}
}

package test02;

import javax.management.RuntimeErrorException;

public class Girl {

	private String name;
	private int age;
	public Girl() {
		
	}
	public Girl(String name,int age) {
		this.setName(name);
		this.setAge(age);
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		int len=name.length();
		if(len<3||len>10) {
			throw new NameFormatException(name+"格式有误应该为3-10");
		}
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		if(age<18||age>40) {
			throw new AgeBoundException(age+"格式有误超出合理范围");
		}
		this.age = age;
	}
	@Override
	public String toString() {
		return "Girl [name=" + name + ", age=" + age + "]";
	}
	
}

public class test {
    public static void main(String [] args) {
    	Scanner sc=new Scanner(System.in);
    	Girl girl=new Girl();//创建对象
    	while(true) {
    	try {
    	System.out.println("请输入姓名：");
        String name=sc.next();
        girl.setName(name);
        //年龄
        System.out.println("请输入年龄：");
        int age=sc.nextInt();
        girl.setAge(age);
        break;
    	} catch (NameFormatException e) {
			e.printStackTrace();
		}catch (AgeBoundException e) {
			e.printStackTrace();
		}
    }
    	System.out.println(girl);
    }
}