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link管理  ›  Java | ==, equals(), compareTo(), equalsIgnoreCase() and compare() - GeeksforGeeks
https://www.geeksforgeeks.org/java-equals-compareto-equalsignorecase-and-compare/
沉着的毛衣
2 月前

Method 1: using == operator

Double equals operator is used to compare two or more than two objects, If they are referring to the same object then return true, otherwise return false. String is immutable in java. When two or more objects are created without new keyword, then both object refer same value. Double equals operator actually compares objects references.


The below example illustrates the use of == for string comparison in Java:

// Compare s1 and s2
// It should return true as they both
// refer to same object in memory
System.out.println(s1 + " == " + s2 + ": "
+ (s1 == s2));
// Compare s1 and s3
// It should return true as they both
// refer to same object in memory
System.out.println(s1 + " == " + s3 + ": "
+ (s1 == s3));
// Compare s2 and s3
// It should return true as they both
// refer to same object in memory
System.out.println(s2 + " == " + s3 + ": "
+ (s2 == s3));
// Compare s1 and s4
// It should return false as they both
// refer to different object in memory
System.out.println(s1 + " == " + s4 + ": "
+ (s1 == s4));

Method 2: Using equals() method

In Java, string equals() method compares the two given strings based on the data / content of the string. If all the contents of both the strings are same then it returns true. If all characters are not matched then it returns false.

Below example illustrate the use of .equals for string comparison in Java:

// It should return true as they both
// have the same content
System.out.println(s1 + " .equals " + s2
+ ": " + s1.equals(s2));
// Compare s1 and s3
// It should return false as they both
// have the different content
System.out.println(s1 + " .equals " + s3
+ ": " + s1.equals(s3));
// Compare s2 and s3
// It should return false as they both
// have the different content
System.out.println(s2 + " .equals " + s3
+ ": " + s2.equals(s3));
// Compare s1 and s4
// It should return true as they both
// have the same content
System.out.println(s1 + " .equals " + s4
+ ": " + s1.equals(s4));

Method 3: Using compareTo() method

In java, Comparable interface compares values and returns an int, these int values may be less than, equal, or greater than 0. The java compares two strings based on the Unicode value of each character in the strings. If two strings are different, then they have different characters at some index that is a valid index for both strings, or their lengths are different, or both.

Assuming index ‘i’ is where characters are different then compareTo() will return firstString.charAt(i)-secondString.charAt(i) .

Below example illustrate the use of .compareTo for string comparison in Java:

// It should return 0 as they both
// have the same ASCII value
System.out.println(s1 + " .compareTo " + s2
+ ": " + s1.compareTo(s2));
// Compare s1 and s3
// It should return -32 as they both
// have the different ASCII value
System.out.println(s1 + " .compareTo " + s3
+ ": " + s1.compareTo(s3));
// Compare s3 and s2
// It should return 32 as they both
// have the different ASCII value
System.out.println(s3 + " .compareTo " + s2
+ ": " + s3.compareTo(s2));
// Compare s1 and s4
// It should return 0 as they both
// have the same ASCII value
System.out.println(s1 + " .compareTo " + s4
+ ": " + s1.compareTo(s4));

Method 4: Using equalsIgnoreCase() method

Java String equalsIgnoreCase() method is much similar to equals() method, except that case is ignored like in above example String object s4 compare to s3 then equals() method return false, but here in case of equalsIgnoreCase() it will return true. Hence equalsIgnoreCase() method is Case Insensitive.

Below example illustrate the use of .equalsIgnoreCase for string comparison in Java:

// It should return true as they both
// have the same content
System.out.println(s1 + " .equalsIgnoreCase " + s2
+ ": "
+ s1.equalsIgnoreCase(s2));
// Compare s1 and s3
// It should return true as they both
// have the same content being case insensitive
System.out.println(s1 + " .equalsIgnoreCase " + s3
+ ": "
+ s1.equalsIgnoreCase(s3));
// Compare s2 and s3
// It should return true as they both
// have the same content being case insensitive
System.out.println(s2 + " .equalsIgnoreCase " + s3
+ ": "
+ s2.equalsIgnoreCase(s3));
// Compare s1 and s4
// It should return true as they both
// have the same content
System.out.println(s1 + " .equalsIgnoreCase " + s4
+ ": "
+ s1.equalsIgnoreCase(s4));

Method 5: Using compare() method

In Java for locale specific comparison, one should use Collator class which is in java.text package. The one most important feature of Collator class is the ability to define our own custom comparison rules.

Below example illustrate the use of compare() method in Java to compare Strings:

// It should return 0 as they both
// have the same ASCII value
System.out.println(s1 + " collator.compare " + s2
+ ": " + collator.compare(s1, s2));
// Compare s1 and s3
// It should return 1
System.out.println(s1 + " collator.compare " + s3
+ ": " + collator.compare(s1, s3));
// Compare s3 and s2
// It should return -1
System.out.println(s3 + " collator.compare " + s2
+ ": " + collator.compare(s3, s2));
// Compare s1 and s4
// It should return 0 as they both
// have the same ASCII value
System.out.println(s1 + " collator.compare " + s4
+ ": " + collator.compare(s1, s4));
Java String equalsIgnoreCase() Method with Examples
In Java, equalsIgnoreCase() method of the String class compares two strings irrespective of the case (lower or upper) of the string. This method returns a boolean value, true if the argument is not null and represents an equivalent String ignoring case, else false. Syntax of equalsIgnoreCase()str2.equalsIgnoreCase(str1);Parametersstr1: A string tha
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Java Integer compareTo() method
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Java long compareTo() with examples
The java.lang.Long.compareTo() is a built-in method in java that compares two Long objects numerically. This method returns 0 if this object is equal to the argument object, it returns less than 0 if this object is numerically less than the argument object and a value greater than 0 if this object is numerically greater than the argument object. Sy
Double.compareTo() Method in Java with Examples
The java.lang.Double.compareTo() is a built-in method in java that compares two Double objects numerically. This method returns 0 if this object is equal to the argument object, it returns less than 0 if this object is numerically less than the argument object and a value greater than 0 if this object is numerically greater than the argument object
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The java.math.BigDecimal.compareTo(BigDecimal bg) method checks for equality of this BigDecimal and BigDecimal object bg passed as parameter. The method considers two equal BigDecimal objects even if they are equal in value irrespective of the scale. Syntax: public int compareTo(BigDecimal bg) Parameters:This function accepts only one BigDecimal ob
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The compareTo() method of java.nio.ByteBuffer class is used to compare one buffer to another. Two byte buffers are compared by comparing their sequences of remaining elements lexicographically, without regard to the starting position of each sequence within its corresponding buffer. Pairs of byte elements are compared as if by invoking Byte.compare
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FloatBuffer compareTo() method in Java With Examples
The compareTo() method of java.nio.FloatBuffer class is used to compare one buffer to another. Two float buffers are compared by comparing their sequences of remaining elements lexicographically, without regard to the starting position of each sequence within its corresponding buffer. Pairs of float elements are compared as if by invoking Float.com
CharBuffer compareTo() method in Java
compareTo() method of java.nio.charBuffer class is used to compare one buffer to another. Two char buffers are compared by comparing their sequences of remaining elements lexicographically, without considering the starting position of each sequence within its corresponding buffer. Pairs of char elements are compared as if by invoking Char.compare(c
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