在自己的类中实例化类型

Question

I cannot figure out what is wrong with this code

class Test {
    int a;
    Test() {
        a=10;
    }

    void new() {
        Test obj1=new Test();
        Test obj2=new Test();
        obj1.a=20;
        obj2.a=30;
    }

    void test(Test obj3,Test obj4) {
        new();
        obj3=obj1;
        obj4=obj2;
    }
}

Please someone explain what exactly is wrong with this code?

Answer 1

Many things are wrong.

For one, new is a reserved keyword, you cannot use it for a method name;

Then, in this function:

void test(Test obj3,Test obj4)
{
    new();
    obj3=obj1;
    obj4=obj2;
}

obj1 and obj2 are not defined. One you get out of your " new() method", your obj1 and obj2 references fall out of scope and cannot be reached anymore;

Finally, obj3 and obj4 would not be affected by this test() method, since Java passes parameters by values, not references:

// doesn't work; when the caller returns, victim is still the same
public void changeInt(int victim)
{
    victim = 0;
}

Answer 2

Change your Code to

class Test
{
int a;
Test obj1;
Test obj2;
Test()
{
a=10;
}
void tester()
{
    obj1=new Test();
    obj2=new Test();
    obj1.a=20;
    obj2.a=30;
}
void test(Test obj3,Test obj4)
{
tester();
obj3=obj1;
obj4=obj2;
}
}

And Try to learn about Scope in java and and new is reserved keyword

Answer 3

obj1 and obj2 are invisible inside the test() method. void new() is illegal method declaration as new is a keyword.

1. You need to declare obj1 and obj2 as instance method or need to pass it somehow to the test() method as parameter.

2. Rename the method void new() to something else.

My suggestions are only to resolve the compilation error . It doesn't account for the logical errors , if any , in the code.