public class StringAsParamOfMethodDemo { 
    public static void main(String[] args) { 
       StringAsParamOfMethodDemo StringAsParamOfMethodDemo = new StringAsParamOfMethodDemo(); 
       StringAsParamOfMethodDemo.testA(); 
    } 
    private void testA() { 
       String originalStr = "original"; 
       System.out.println("Test A Begin:"); 
       System.out.println("The outer String: " + originalStr); 
       simpleChangeString(originalStr); 
       System.out.println("The outer String after inner change: " + originalStr); 
       System.out.println("Test A End."); 
       System.out.println(); 
    } 
    public void simpleChangeString(String original) { 
       original = original + " is changed!"; 
       System.out.println("The changed inner String: " + original); 
    } 
} 

Test A Begin:
The outer String: original
The changed inner String: original is changed!
The outer String after inner change: original
Test A End.

int number = 0; 

changeNumber(number) {number++}; //改变送进的int变量 

StringBuffer strBuf = new StringBuffer(“original”); 

changeStringBuffer(strBuf) {strbuf.apend(“ is changed!”)} //改变送进的StringBuffer变量 

private void testB() { 
   String originalStr = new String("original"); 
   System.out.println("Test B Begin:"); 
   System.out.println("The outer String: " + originalStr); 
   changeNewString(originalStr); 
   System.out.println("The outer String after inner change: " + originalStr); 
   System.out.println("Test B End:"); 
   System.out.println(); 
   } 
public void changeNewString(String original) { 
   original = new String(original + " is changed!"); 
   System.out.println("The changed inner String: " + original); 
   } 

Test B Begin:
The outer String: original
The changed inner String: original is changed!
The outer String after inner change: original
Test B End.

    private void testC() { 
       String originalStr = new String("original"); 
       System.out.println("Test C Begin:"); 
       System.out.println("The outer String: " + originalStr); 
       changeStrWithMethod(originalStr); 
       System.out.println("The outer String after inner change: " + originalStr); 
       System.out.println("Test C End."); 
       System.out.println(); 
} 
    private static void changeStrWithMethod(String original) { 
       original = original.concat(" is changed!"); 
       System.out.println("The changed inner String: " + original); 
}

Test C Begin:
The outer String: original
The changed inner String: original is changed!
The outer String after inner change: original
Test C End.

  public String(String original) { 
        int size = original.count; 
        char[] originalValue = original.value; 
        char[] v; 
        if (originalValue.length > size) { 
          // The array representing the String is bigger than the new 
          // String itself.  Perhaps this constructor is being called 
          // in order to trim the baggage, so make a copy of the array. 
          int off = original.offset; 
              v = Arrays.copyOfRange(originalValue, off, off+size); 
        } else { 
          // The array representing the String is the same 
          // size as the String, so no point in making a copy. 
          v = originalValue; 
        } 
        this.offset = 0; 
        this.count = size; 
        this.value = v; 
}