Exception handling in Java-javaTutorial-php.cn

Exception handling in Java

黄舟

Release： 2017-02-22 10:05:58

Original

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1. Example 1
//try-catch handles exceptions

public class Error {

	public static void main(String[] args) {
		
		int num1=34,num2=0;
		
		//使用try包裹住会产生异常的代码段
		
		try{
		
			System.out.println(num1/num2);
			
		}
		
		//使用catch去处理对应的异常
		
		catch(ArithmeticException error){
		
		//处理方法
		
			System.err.println("运算错误，除数不能为0！");
			
		}
		
		System.out.println("程序运行结束！");
		
	}
}

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Result verification:
Operation error, the divisor cannot be 0!
The program is finished!
2. Example 2

import java.util.InputMismatchException;

import java.util.Scanner;
 
public class Error {
 
    public static void main(String[] args) {
    	
        Scanner input = new Scanner(System.in);
        
        System.out.println("请输入第一个数字：");
        
        //使用try包裹住会产生异常的代码段
        
        try{
            int num1=input.nextInt();
            
            System.out.println("请输入第二个数字：");
            
            int num2=input.nextInt();
            
            System.out.println(num1/num2);
        }
        
        //使用catch去处理对应的异常
        
        catch(ArithmeticException error1){
        	
            //处理方法
        	
            System.err.println("运算错误，除数不能为0！");
            
        }catch(InputMismatchException error2){
        	
            System.err.println("请输入正确的数字！");
        }
        
        System.out.println("程序运行结束！");
         
    }
}

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Result verification:

Result one:
Please enter the first number:
123
Please enter the second number:
123
1
The program is finished!
Result 2:
Please enter the first number:
123
Please enter the second number:
b
Please enter the correct number!
The program is finished!

Result 3:
Please enter the first number:
123
Please enter the second number:
0
Operation error, divisor It cannot be 0!
The program is finished!

3. Example 3
//Convert user input string to integer
3.1

public class Error {
		
		String str;
		
		public Error(String str) {
			
			this.str = str;
		}

			public  String Transform(){
				try{
					
					int num = Integer.parseInt(str);
					
				}catch(NumberFormatException num){
					
					System.out.println("字符串转整型，请输入正确的数字:");
					
				}catch(Exception e){
					
				}
				return str;
		}		
}

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//Write a test class, call the data type conversion method, and pass the parameters "Good!" and 20

public class ErrorDemo {
	
	public static void main(String[] args) {
		
		Error er = new Error("Good!");
		
		er.Transform();
		
		System.out.println(er.str);

	}

}

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String conversion Integer, please enter the correct number:
Good!
3.2

public class Error {
         
        int num = 0;
         
        public Error() {
            
          
        }
        
        public Error(int num) {
             
            this.num = num;
        }
 
        public  int TransformtoInt(String str){
              
        	try{
                     
                 int num1 = Integer.parseInt(str);
                     
                }catch(NumberFormatException num){
                     
                    System.err.println("字符串转整型，请输入正确的数字:");
                     
                }catch(Exception error){
                     
                	error.printStackTrace();
                	
                }
        return num;
        }      
}

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import java.util.Scanner;

public class ErrorDemo {
     
    public static void main(String[] args) {
   
    	Scanner input = new Scanner(System.in);
        
    	System.out.println("请输入一个数字：");
    	
    	String str = input.next();
    	
    	Error toInt = new Error();
    	
        toInt.TransformtoInt(str);
         
        System.out.println(str);
 
    }
 
}

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Verification:

Please enter a number:
123
123

Please enter a number:
abc
Convert string to integer, please enter Correct number:
abc

4. Example 4
//[b]throws, throw throws exception[/b]

public class Error {
         
    String sex ;
 
    public Error() {
       
    }
 
    public String getSex() {
    	
        return sex;
        
    }
 
    public void setSex(String sex) throws Exception {
         
            if(sex.equals("男")|sex.equals("女")){
            	
                this.sex = sex;
                
            }else{
         
                throw new Exception("性别必须为男或者女！");
            }              
    }          
}

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public class ErrorDemo {
 
     
    public static void main(String[] args) {
     
        Error er = new Error();
        
        try{
        	
            er.setSex("熊");
            
        }catch(Exception error){
        	
            error.printStackTrace();
        }
        
        System.out.println("程序结束");
 
    }
 
}

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java.lang.Exception: Gender must be male or female!
at Error.setSex(Error.java:22)
at ErrorDemo.main(ErrorDemo.java:9)
End of program

5、
Custom exception
//Create Excption subclass to inherit [b]ExcptionParent class[/b]

//创建类

public class Error {
         
    String sex ;
 
    public Error() {
       
    }
 
    public String getSex() {
    	
        return sex;
        
    }
 
    public void setSex(String sex) throws Exception {
         
            if(sex.equals("男")|sex.equals("女")){
            	
                this.sex = sex;
                
            }else{
         
                throw new ExceptionDemo("性别必须为男或者女！");
            }              
    }          
}

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//创建ExceptionDemo子类

public class ExceptionDemo extends Exception {

	public ExceptionDemo() {
		super();
		
	}

	public ExceptionDemo(String message) {
		super(message);
		
	}
	
}

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//创建测试类

import java.util.Scanner;

public class ErrorDemo {
 
     
    public static void main(String[] args) {
     
        Error er = new Error();
        
        try{
        	
        	Scanner next = new Scanner(System.in);
        	
        	System.out.println("请输入性别：");
        	
            er.setSex(next.next());
            
        }catch(Exception error){
        	
            error.printStackTrace();
        }
        
        System.out.println("程序结束！");
 
    }
 
}

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Result verification:
Please enter gender:
Male
End of program!

Please enter your gender:

nan
ExceptionDemo: 性别必须为男或者女！
at Error.setSex(Error.java:23)
at ErrorDemo.main(ErrorDemo.java:10)

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The program is over!

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