java face questions , seek guidance

Great God

  public class TestStr {
  	public String str="1234";
  	public Integer number=10;
  	
  	public void changeStr(String s){
  		s="hello";
  	}
  	public void changeInt(Integer i){
  		i=20;
  	}
  	
  	public static void main(String[] arg0) {
  		TestStr test = new TestStr();
  		test.changeStr(test.str);
  		test.changeInt(test.number);
  		System.out.println(test.str);
  		System.out.println(test.number);
  	}
  
  }
  

output is:
1234
10
Why is this ? Why changeStr can not change the value of str , very puzzled . .
------ Solution ---------------------------------------- ----
can say specifically what     

java in method calls , arguments passed to its value corresponding formal parameter , method execution parameter value change does not affect the value of the argument .
------ Solution ---------------------------------------- ----
Java 's value is passed , the method parameters and arguments occupy different memory space, method invocation , the arguments to the method copies the value to the parameter , the parameter in the method for operating without will affect the argument . . . . Overall in JAVA method can not be modified to achieve change in the value of the formal parameter method arguments worthy purpose
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value transfer problems
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can say specifically what
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Oh, and understood it. Extremely grateful ! !
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understand is that the parameter is actually a copy of the argument is not it ?         
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further questions, in C or C + + it is allowed to do this ?
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c is not object-oriented
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c + + have passed by reference