引用参数传递
引用参数传递（call-by-reference parameter passing）

public class Test {public int a ;public int b ;@Overridepublic String toString() {// TODO Auto-generated method stubreturn this.getClass().getSimpleName()+"["+a+","+b+"]";}}

public static Test changeTest(Test test){test.b = 4;test = null;return test;}public static void testCallByReferenceParameterPassing(){Test t = new Test();t.a = 1;t.b = 2;Test t2 = t;t2.a = 3;Test t3 = changeTest(t);System.out.println(t);System.out.println(t2);System.out.println(t3);}

打印结果：
Test[3,4]
Test[3,4]
null