Java引用传递问题

public class TestInnerClass {


    public static void populateVal(InnerClassA a) {
        if(a == null) {
            a = new InnerClassA();
        }
        a.setId(1);
        a.setName("aa");
    }

    public static class InnerClassA {
        private int id;
        private String name;

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "InnerClassA{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }
}

public class MyTest {
    public static void main(String[] args) {
        test1();
    }

    private static void test1() {
        TestInnerClass.InnerClassA aCla = null;
        set(aCla);
        System.out.println(aCla);
        myprint(aCla);
    }

    private static void myprint(TestInnerClass.InnerClassA aCla) {
        System.out.println(aCla);
    }

    public static void set(TestInnerClass.InnerClassA aCla) {
        TestInnerClass.populateVal(aCla);
    }

}

// 输出
null
null

// 可解决
TestInnerClass.InnerClassA aCla = new TestInnerClass.InnerClassA();