[移动开发]java测试try-return和finally-return

测试try-eturn，finally里++

使用jdk8进行测试

public class Sample {

    public static void main(String[] args) throws Throwable {
        int retInt = testInt();
        System.out.println("result:" + retInt);
        System.out.println("----------------");
        String retStr = testString();
        System.out.println("result:" + retStr);
        System.out.println("----------------");
        Map<String, String> retMap = testMap();
        System.out.println("result:" + retMap.get("test"));
    }

    private static int testInt() {
        int i = 1;
        try {
            i++;
            System.out.println("try:" + i);
            return i;
        } finally {
            i++;
            System.out.println("finally:" + i);
        }
    }

    private static String testString() {
        String i = "test";
        try {
            i = "test1";
            System.out.println("try:" + i);
            return i;
        } finally {
            i = "test2";
            System.out.println("finally:" + i);
        }
    }

    private static Map<String, String> testMap() {
        Map<String, String> map = new HashMap<>();
        try {
            map.put("test", "test1");
            System.out.println("try:" + map.get("test"));
            return map;
        } finally {
            map.put("test", "test2");
            System.out.println("finally:" + map.get("test"));
        }
    }
}

输出

try:2
finally:3
result:2
----------------
try:test1
finally:test2
result:test1
----------------
try:test1
finally:test2
result:test2

查看反编译后的代码

public class Sample {
    public Sample() {
    }

    public static void main(String[] args) throws Throwable {
        int retInt = testInt();
        System.out.println("result:" + retInt);
        System.out.println("----------------");
        String retStr = testString();
        System.out.println("result:" + retStr);
        System.out.println("----------------");
        Map<String, String> retMap = testMap();
        System.out.println("result:" + (String)retMap.get("test"));
    }

    private static int testInt() {
        int i = 1;

        int var1;
        try {
            ++i;
            System.out.println("try:" + i);
            var1 = i;
        } finally {
            ++i;
            System.out.println("finally:" + i);
        }

        return var1;
    }

    private static String testString() {
        String i = "test";

        String var1;
        try {
            i = "test1";
            System.out.println("try:" + i);
            var1 = i;
        } finally {
            i = "test2";
            System.out.println("finally:" + i);
        }

        return var1;
    }

    private static Map<String, String> testMap() {
        HashMap map = new HashMap();

        HashMap var1;
        try {
            map.put("test", "test1");
            System.out.println("try:" + (String)map.get("test"));
            var1 = map;
        } finally {
            map.put("test", "test2");
            System.out.println("finally:" + (String)map.get("test"));
        }

        return var1;
    }
}

结论：

java编译时做了代码优化，使用var1变量替换了原来的返回值。

测试try-return，finally里++后又return

public class Sample {

    public static void main(String[] args) throws Throwable {
        int retInt = testInt();
        System.out.println("result:" + retInt);
        System.out.println("----------------");
        String retStr = testString();
        System.out.println("result:" + retStr);
        System.out.println("----------------");
        Map<String, String> retMap = testMap();
        System.out.println("result:" + retMap.get("test"));
    }

    private static int testInt() {
        int i = 1;
        try {
            i++;
            System.out.println("try:" + i);
            return i;
        } finally {
            i++;
            System.out.println("finally:" + i);
            return i;
        }
    }

    private static String testString() {
        String i = "test";
        try {
            i = "test1";
            System.out.println("try:" + i);
            return i;
        } finally {
            i = "test2";
            System.out.println("finally:" + i);
            return i;
        }
    }

    private static Map<String, String> testMap() {
        Map<String, String> map = new HashMap<>();
        try {
            map.put("test", "test1");
            System.out.println("try:" + map.get("test"));
            return map;
        } finally {
            map.put("test", "test2");
            System.out.println("finally:" + map.get("test"));
            return map;
        }
    }
}

输出

try:2
finally:3
result:3
----------------
try:test1
finally:test2
result:test2
----------------
try:test1
finally:test2
result:test2

查看反编译后的代码

public class Sample {
    public Sample() {
    }

    public static void main(String[] args) throws Throwable {
        int retInt = testInt();
        System.out.println("result:" + retInt);
        System.out.println("----------------");
        String retStr = testString();
        System.out.println("result:" + retStr);
        System.out.println("----------------");
        Map<String, String> retMap = testMap();
        System.out.println("result:" + (String)retMap.get("test"));
    }

    private static int testInt() {
        int i = 1;

        try {
            ++i;
            System.out.println("try:" + i);
        } finally {
            ++i;
            System.out.println("finally:" + i);
            return i;
        }
    }

    private static String testString() {
        String i = "test";

        try {
            i = "test1";
            System.out.println("try:" + i);
        } finally {
            i = "test2";
            System.out.println("finally:" + i);
            return i;
        }
    }

    private static Map<String, String> testMap() {
        HashMap map = new HashMap();

        try {
            map.put("test", "test1");
            System.out.println("try:" + (String)map.get("test"));
        } finally {
            map.put("test", "test2");
            System.out.println("finally:" + (String)map.get("test"));
            return map;
        }
    }
}

结论：

java编译时做了代码优化，只使用finally里的return。

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