EXCEPTION
java 中异常返回时机 #
example #
// finally语句在return语句执行之后return返回之前执行的
public int exp1(){
int b = 20;
try {
System.out.println("try block");
return b += 80;
}
catch (Exception e) {
System.out.println("catch block");
}
finally {
System.out.println("finally block");
if (b > 25) {
System.out.println("b>25, b = " + b);
}
}
return b;
}
output:
try block
finally block
b>25, b = 100
100
// finally块中的return语句会覆盖try块中的return返回
public int exp2() {
int b = 20;
try {
System.out.println("try block");
return b += 80;
} catch (Exception e) {
System.out.println("catch block");
} finally {
System.out.println("finally block");
if (b > 25) {
System.out.println("b>25, b = " + b);
}
return 200;
}
// return b;
}
output:
try block
finally block
b>25, b = 100
200
// 如果finally语句中没有return语句覆盖返回值,那么原来的返回值可能因为finally里的修改而改变也可能不变
public int exp3() {
int b = 20;
try {
System.out.println("try block");
return b += 80;
} catch (Exception e) {
System.out.println("catch block");
} finally {
System.out.println("finally block");
if (b > 25) {
System.out.println("b>25, b = " + b);
}
b = 150;
}
return 2000;
}
output:
try block
finally block
b>25, b = 100
100
public Map<String, String> exp3_1() {
Map<String, String> map = new HashMap();
map.put("KEY", "INIT");
try {
map.put("KEY", "TRY");
return map;
}
catch (Exception e) {
map.put("KEY", "CATCH");
}
finally {
map.put("KEY", "FINALLY");
map = null;
}
return map;
}
output:
FINALLY
// try块里的return语句在异常的情况下不会被执行(参考中的例子有错误)
public int exp4() {
int b = 20;
try {
System.out.println("try block");
b = b / 0;
return b += 80;
} catch (Exception e) {
b += 15;
System.out.println("catch block");
} finally {
System.out.println("finally block");
if (b > 25) {
System.out.println("b>25, b = " + b);
}
b += 50;
}
return 204;
}
output:
try block
catch block
finally block
b>25, b = 35
204
// 当发生异常后,catch中的return执行情况与未发生异常时try中return的执行情况完全一样
public int exp5() {
int b = 20;
try {
System.out.println("try block");
b = b /0;
return b += 80;
} catch (Exception e) {
System.out.println("catch block");
return b += 15;
} finally {
System.out.println("finally block");
if (b > 25) {
System.out.println("b>25, b = " + b);
}
b += 50;
}
//return b;
}
output:
try block
catch block
finally block
b>25, b = 35
35
// catch中的return先计算然后传值到finally中最后finally直接返回,也符合情况1。
public int exp6() {
int b = 20;
try {
System.out.println("try block");
b = b /0;
return b += 80;
} catch (Exception e) {
System.out.println("catch block");
return b += 15;
} finally {
System.out.println("finally block");
if (b > 25) {
System.out.println("b>25, b = " + b);
}
return b += 50;
}
//return b;
}
output:
try block
catch block
finally block
b>25, b = 35
85
字节码查看异常执行顺序 #
reference #
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