java到底是值传递还是引用传递？

对于基本数据类型，可以记住是值传递，即传进去的参数做任何修改不会影响外面。

对于类，是引用传递，传进函数的对象，在函数中做的任何动作都会一直生效，能带到外面来。

有个特殊情况：字符串，它是类但它的现象又是值传递，一般人考试就爱考这个！不得不说，有些人就喜欢问茴香的茴字有多少种写法，屁用没有！

public class Test {

    public int a = 0;

    public static void testForValue(int i) {
        i++;
    }

    public static void testForReferenceTest(Test test) {
        test.a = 10;
    }

    public static void testForReferenceString(String str) {
        str = "abc";
    }

    public static void main(String[] args) {
        // test value
        int i = 0;
        System.out.println("before value test: i=" + i);
        Test.testForValue(i);
        System.out.println("after value test: i=" + i);

        System.out.println("===================================================");

        // test reference
        Test test = new Test();
        System.out.println("before normal reference test: test.a=" + test.a);
        Test.testForReferenceTest(test);
        System.out.println("after normal reference test: test.a=" + test.a);

        System.out.println("===================================================");
        // test String reference
        String str = "123";
        System.out.println("before String reference test: str=" + str);
        Test.testForReferenceString(str);
        System.out.println("after String reference test: str=" + str);

    }

}

输出结果

before value test: i=0
after value test: i=0
===================================================
before normal reference test: test.a=0
after normal reference test: test.a=10
===================================================
before String reference test: str=123
after String reference test: str=123