Java Some validation of assignment symbols for string classes

As we all know, many Java books say that the contents of a string object cannot be modified, but in practice the assignment notation can still be used in the created String class object, as shown in the following code:

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 1     String s1 =  "ABS"; 2      string s2 =  "ABS";  3     system.out.println ("Before change:" );  4     system.out.println ("s1 is " +s1); 5      system.out.println ("s2 is " +s2);  6     system.out.println ( "s1 == s2 is "  +  (S1 == S2));  7     s1  = s1.replace (' A ', ' C ');  8     system.out.println ("After change:") ;  9     system.out.println ("s1 is " +s1);10      system.out.println ("s2 is " +s2); 11     system.out.println ("s1 ==  s2 is  " +  (S1 == S2));

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The results of the program running are as follows:

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As can be seen from the results:

S1 can be modified with an assignment symbol, and no error will be given at this time. At first, S1 and S2 point to the same address. When S1 is modified,s2 's content does not change,s1 and S2 will no longer point to the same address. At this point,S1 should have re-created an object.

Here to point out is the statement s1.replace (' A ', ' C '); Returns a new string and does not change the contents of the original string. If you do not simply run S1.replace (' A ', ' C '), the contents of S1 will not change.

If you connect a string class object that you have created with an assignment symbol to another string class object, the effect will be different, as shown in the code:

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 1 String s1 =  "ABS"; 2  3 string s2 =  "ABS";  4  5 String s3 = new String  ("abs"); 6  7  System.out.println ("Before change:");  8  9 system.out.println ("s1 is " +s1); 10 11 system.out.println ("s2 is " +s2); 12 13 system.out.println ("s3 is  "+s3"); 14 15 system.out.println ("s1 == s2 is "  +  (S1 == S2)); 16 17 system.out.println ("s2 == s3 is "  +  (S2 == S3)); 18  19 s3 = s1;20 21 system.out.println ("After change:");22 23  System.out.println ("s1 is " +s1); 24 25 system.out.println ("s2 is " +s2); 26 27  system.out.println ("s3 is " +S3); 28 29 system.out.println ("S1 == s2 is   " +  (S1 == S2) 30 31 system.out.println ("s2 == s3 is "  +  (s2 ==  S3));

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The results of the code run are as follows:

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As you can see, the original S1 and S3 do not point to the same location, But when s3 = S1 is executed, S3 points to the S1 address, at which point s2,s3 points to the same address. According to the Java recycling mechanism, the object of the address to which the original S3 is pointing should be recycled.

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Java Some validation of assignment symbols for string classes