关于try-catch、throw、finally在异常时的执行顺序

女爷i 2022-07-13 10:14 187阅读 0赞

package test;
    //jdk 1.8
    public class TestException1 {
    
    	
    	/**
    	 * catch中的return和throw是不能共存的(无论谁先谁后都编译不通过)
    	 * 如果只throw e，则必须try-catch捕捉异常e或用throws抛出异常e
    	 * 如果只return ，则在catch段正常返回值
    	 */
    	int testEx0(){
    		boolean ret = true;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return 0;
    		} catch (Exception e) {
    			System.out.println("testEx, catch exception");
    			ret = false;
    			return -1;
    			throw e;
    		}
    	}
    	/**
    	 * 在finally中的return和throw是不能共存的(无论谁先谁后都编译不通过)
    	 * 如果只throw e，则必须try-catch捕捉异常e或用throws抛出异常e
    	 * 如果只return ，则在catch段正常返回值
    	 */
    	int testEx00(){
    		int  ret = 0;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return ret;
    		} catch (Exception e) {
    			System.out.println("testEx, catch exception");
    			ret = -1;
    		}finally{
    			ret = 1;
    			System.out.println("testEx, finally; return value=" + ret);
    			throw e;
    			return ret;
    		}
    	}
    	/**
    	 * 结果：
    	 	testEx, catch exception
    		testEx, finally; return value=false
    		false
    		结论：在finally里没有return的时候：先执行finally的语句，再执行catch的return
    	 */
    	boolean testEx01(){
    		boolean ret = true;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return true;
    		} catch (Exception e) {
    			System.out.println("testEx, catch exception");
    			ret = false;
    			return ret;
    		}finally{
    			System.out.println("testEx, finally; return value=" + ret);
    			
    		}
    	}
    	/**
    	 * 	结果：
    	 * 	testEx, catch exception
    		testEx, finally; return value=1
    		1
    		结论：在finally里有return的时候：先执行finally的语句和return，忽略catch的return
    	 */
    	int testEx02(){
    		int ret = 0;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return ret;
    		} catch (Exception e) {
    			ret = -1;
    			System.out.println("testEx, catch exception");
    			return ret;
    		}finally{
    			ret = 1;
    			System.out.println("testEx, finally; return value=" + ret);
    			return ret;
    		}
    	}
    	/**
    	 * 编译能通过，
    	 * 但运行时抛异常（当然也没有返回值）
    	 * @return
    	 */
    	boolean testEx03(){
    		boolean ret = true;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return true;
    		} catch (Exception e) {
    			System.out.println("testEx, catch exception");
    			ret = false;
    			throw e;
    		}finally{
    			System.out.println("testEx, finally; return value=" + ret);
    			
    		}
    	}
    	/**
    	 * 编译不能通过（必须加throws主动抛异常，或try-catch捕捉，）
    	 * 但运行时抛异常（当然也没有返回值）
    	 * @return
    	 * @throws Exception 
    	 */
    	boolean testEx031(){
    		boolean ret = true;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return true;
    		} catch (Exception e) {
    			System.out.println("testEx, catch exception");
    			ret = false;
    			throw new Exception(e);
    		}finally{
    			System.out.println("testEx, finally; return value=" + ret);
    			
    		}
    	}
    	/**
    	 * 结果：
    	 * 	testEx, catch exception
    		testEx, finally; return value=1
    		1 
    		结论：
    		函数在finally里正常返回return的值，无异常，显然catch中的throw被忽略
    	 */
    	int testEx04(){
    		int ret = 0;
    		try {
    			int c = 12 / 0;
    			System.out.println("testEx,successfully");
    			return ret;
    		} catch (Exception e) {
    			System.out.println("testEx, catch exception");
    			ret = -1;
    			throw e;
    		}finally{
    			ret = 1;
    			System.out.println("testEx, finally; return value=" + ret);
    			return ret;
    		}
    	}
    	
    	public static void main(String[] args) {
    		try {
    			System.out.println(new TestException1().testEx0());
    			//System.out.println(new TestException1().testEx00());
    			//System.out.println(new TestException1().testEx01());
    			//System.out.println(new TestException1().testEx02());
    			//System.out.println(new TestException1().testEx03());
    			//System.out.println(new TestException1().testEx031());
    			//System.out.println(new TestException1().testEx04());
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    	
    }