class returntest
{
public static void main(String...args)
{
String name1 = "Test";
String s = new String("Test");
StringBuilder sb = new StringBuilder("Test");
System.out.println(name1.equals(sb)); //Line 1
System.out.println(name1.equals(s)); //Line 2
System.out.println(s.equals(sb)); // Line 3
System.out.println(s.equals(name1)); //Line 4
}
}
The following is the output
false
true
false
true
Line 1 returns and Line 3 returns false.
I dont understand why compiler does not think "name1" and "sb" as containing the same value
Similarly compiler does not think "s" and "sb" as containing the same string (both are non-primitives).
Can someone explain the line1 and line3 output ?
Because they both are Different objects
.
String object!= StringBuilder object.
But,Your doubt is
name1.equals(s) returning true
Because in String class equals method ovverided in such a way.
And to get the desired output convert your StringBuilder
to String
.
System.out.println(s.equals(sb.toString())); //return true.
If you see the Source code of String#equals()
1012 public boolean equals(Object anObject) {
1013 if (this == anObject) {
1014 return true;
1015 }
1016 if (anObject instanceof String) { //key line
1017 String anotherString = (String)anObject;
1018 int n = count;
1019 if (n == anotherString.count) {
1020 char v1[] = value;
1021 char v2[] = anotherString.value;
1022 int i = offset;
1023 int j = anotherString.offset;
1024 while (n-- != 0) {
1025 if (v1[i++] != v2[j++])
1026 return false;
1027 }
1028 return true;
1029 }
1030 }
1031 return false;
1032 }
The line if (anObject instanceof String) {
always returns false incase if you pass StringBuilder
.
The reason for the two false
cases is that this is how the respective equals(Object)
methods are specified to work.
For String.equals(Object)
, the javadoc says this:
"Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object."
For StringBuilder.equals(Object)
, the equals
method is inherited from Object
, where the javadoc says this:
"returns true if this object is the same as the obj argument; false otherwise."
So on Line #1 and Line #3, String.equals(Object)
returns false
because sb
is not a String
.
And if you reversed it and called sb.equals(name1)
or sb.equals(s)
you would get false
also ... because sb.equals(...)
is testing for the same object.
I dont understand why compiler does not think "name1" and "sb" as containing the same value
As you can see, it is nothing to do with the compiler ... and everything to do with the way that the equals
method is specified.
String.equals compares not contents but objects
public boolean equals(Object anObject) {
if (this == anObject) {
return true;
}
if (anObject instanceof String) {
...
}
return false;
}
StringBuilder does not override equals at all and inherits Object.equals
public boolean equals(Object obj) {
return (this == obj);
}
Use sb.toString()
instead of direct sb
directly.
This compares this string to the specified object.
System.out.println(name1.equals(sb.toString())); //Line 1
System.out.println(name1.equals(s)); //Line 2
System.out.println(s.equals(sb.toString())); // Line 3
System.out.println(s.equals(name1)); //Line 4
This returns true value for all the line.
true
true
true
true
Question Issue on Comparing String and Object value Java has been duplicated to this question so posting the answer here
Since String
, StringBuffer
and StringBuilder
are implementing CharSequence
you can check the content's equality by using contentEquals
method in String
"java".contentEquals(new StringBuffer("java")); // true
"java".contentEquals(new StringBuilder("java")); // true
.equals()
checks if two objects are equal. This typically involves checking if both objects are of the same type.
If you only want to check if the values are equal, you should use sb.toString()
.
System.out.println(s.equals(sb.toString()));
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