try-catch-finally问题
9个例子，弄清楚try-catch-finally-return
例1
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
return t;
} catch (Exception e) {
t = "catch";
return t;
} finally {
t = "finally";
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回结果：try
例2
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
return t;
} catch (Exception e) {
t = "catch";
return t;
} finally {
t = "finally";
return t;
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：finally
例3
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
Integer.parseInt(null);
return t;
} catch (Exception e) {
t = "catch";
return t;
} finally {
t = "finally";
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：catch
例4
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
Integer.parseInt(null);
return t;
} catch (Exception e) {
t = "catch";
return t;
} finally {
t = "finally";
return t;
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：finally
例5
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
Integer.parseInt(null);
return t;
} catch (Exception e) {
t = "catch";
Integer.parseInt(null);
return t;
} finally {
t = "finally";
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：
Exception in thread "main" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:454)
at java.lang.Integer.parseInt(Integer.java:527)
at com.it.test.TryCatchFinally.test(TryCatchFinally.java:20)
at com.it.test.TryCatchFinally.main(TryCatchFinally.java:29)
例6
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
Integer.parseInt(null);
return t;
} catch (Exception e) {
t = "catch";
Integer.parseInt(null);
return t;
} finally {
t = "finally";
return t;
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：
finally
例7
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
Integer.parseInt(null);
return t;
} catch (NullPointerException e) {
t = "catch";
return t;
} finally {
t = "finally";
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：
Exception in thread "main" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:454)
at java.lang.Integer.parseInt(Integer.java:527)
at com.it.test.TryCatchFinally.test(TryCatchFinally.java:16)
at com.it.test.TryCatchFinally.main(TryCatchFinally.java:27)
例8
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
Integer.parseInt(null);
return t;
} catch (NullPointerException e) {
t = "catch";
return t;
} finally {
t = "finally";
return t;
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：finally
例9
public class TryCatchFinally {
@SuppressWarnings("finally")
public static final String test() {
String t = "";
try {
t = "try";
return t;
} catch (Exception e) {
t = "catch";
return t;
} finally {
t = "finally";
String.valueOf(null);
return t;
}
}
public static void main(String[] args) {
System.out.print(TryCatchFinally.test());
}
}
返回值：
Exception in thread "main" java.lang.NullPointerException
at java.lang.String.(String.java:168)
at java.lang.String.valueOf(String.java:2861)
at com.it.test.TryCatchFinally.test(TryCatchFinally.java:21)
at com.it.test.TryCatchFinally.main(TryCatchFinally.java:27)
结论：
finally前语句(try,catch)中有return，那么会先保存临时值，finlly结束后会返回临时值，finally中的return优先前语句中的return
try、catch、finally语句中，如果只有try语句有return返回值，此后在catch、finally中对变量做任何的修改，都不影响try中return的返回值。
try、catch中有返回值，而try中抛出的异常恰好与catch中的异常匹配，则返回catch中的return值。
如果finally块中有return 语句，则返回try或catch中的返回语句忽略。
-
如果finally块中抛出异常，则整个try、catch、finally块中抛出异常.并且没有返回值
所以在使用try、catch、finally语句块时需要注意以下几点：
- 尽量在try或者catch中使用return语句。通过finally块中达到对try或者catch返回值修改是不可行的。
- finally块中避免使用return语句，因为finally块中如果使用return语句，会显示的忽略掉try、catch块中的异常信息，屏蔽了错误的发生。
- finally块中避免再次抛出异常，否则整个包含try语句块的方法回抛出异常，并且会忽略掉try、catch块中的异常。
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原文链接：https://blog.csdn.net/mxd446814583/article/details/80355572