static and non-static variable

[Kee Kee moon]

This is a dum question, but I could not figure it out. Please shed a light.
Why are get str: null and test2Str: null, if I use non-static for private String str2; in class Test2.

Only If I use static, the string will not be null. This occurs in my project, I cannot use static. Please help.

package test1;

import test2.Test2;
import test3.Test3;

public class Test {
	public void testExample() {
		Test2 test2 = new Test2();
		test2.setTest2("this is a test2");
	}
	public static void main(String [] args) {
		Test test = new Test();
		test.testExample();
		Test3 test3 = new Test3();
		test3.test3Example();
	}
}

the output as below:

set string: this is a test2
get str2: null
test2Str: null



--------------------------------------------------------------

package test2;

public class Test2 {
	private String str2;
	
	public void setTest2(String string) {
		System.out.println("set string: " + string);
		str2 = string;
		
	}
	public String getTest2() {
		System.out.println("get str2: " + this.str2);
		return str2;
	}
}

-------------------------------------------------------------------------

package test3;

import test2.Test2;

public class Test3 {
	public void test3Example() {
		Test2 test2 = new Test2();
		String test2Str = test2.getTest2();
		System.out.println("test2Str: " + test2Str);
	}

}

[Tyson Lindner]

The reason is that your methods is Test and Test3 are each creating their own Test2 objects and references. The string value from the Test2 object in the Test3 object is never set so it has the default value of null.

It might help if you rename all your classes and methods, as it is its extremely confusing for anyone.

[Kee Kee moon]

Thanks.
My question is. If I use static, I can get the string value, but I cannot use static.
I know I did not init the string and will get null. I got stuck with static and non-static.
Thanks again.

[Ulf Dittmer]

Kee Kee moon wrote:If I use static, I can get the string value, but I cannot use static. I know I did not init the string and will get null. I got stuck with static and non-static.

I think you're confusing yourself with all that talk about static and non-static.

As Tyson said, the string is never set in Test2 instance used in Test3, so it is null. That has nothing at all to do with whether that field is static or non-static, the result would be the same in either case.

[Tyson Lindner]

Ulf Dittmer wrote:
As Tyson said, the string is never set in Test2 instance used in Test3, so it is null. That has nothing at all to do with whether that field is static or non-static, the result would be the same in either case.

No, if str2 is static the output is always "this is a test2". A new object being initialized won't change the current static value back to the default value. To further answer OP's question, a static modifier means that when the value changes it changes for all instances of that object.

If you want to ensure that all objects have a non-static value that is the same, you have to iterate through every object and check/set that value.

[Kee Kee moon]

Tyson Lindner wrote:

Ulf Dittmer wrote:
As Tyson said, the string is never set in Test2 instance used in Test3, so it is null. That has nothing at all to do with whether that field is static or non-static, the result would be the same in either case.

No, if str2 is static the output is always "this is a test2". A new object being initialized won't change the current static value back to the default value. To further answer OP's question, a static modifier means that when the value changes it changes for all instances of that object.

If you want to ensure that all objects have a non-static value that is the same, you have to iterate through every object and check/set that value.

Thank you.
I cannot use static, but I need to get the value. Can you give me some examples how to work it out. Thanks again.
My friend and I have been debated about this, in the beginning I was clear about this. As now, I am really confused and feel dumb.

[Tyson Lindner]

Kee Kee moon wrote:
I cannot use static, but I need to get the value.

I'm not sure what you mean by "get" the value. If one object has a value, for another object to "get" that value (if its not static) you have to manually pass that value to that object. So generally that value must be passed to your new object in the form of a constructor or method.

Again, it will help clarify what you are trying to accomplish or demonstrate if you redesign your code.