Java object comparer and cloning

I. Comparator comparable and comparator

The previous blog introduced the tool class arrays tool class . We can call the Arrays.sort () function on an array of basic types to sort the array. Sorting operations are often used in daily development. Then can the string class and custom classes be sorted using Arrays.sort (). Let's try it as follows:

Java code

Public class Mystring {

4. Public Static voidMain (string[] args) {

8. String []a={"Morning","Noon","Afternoon","Evening","Evening"};

12. Person[] b={ newperson ("small white",newperson ("Black",19 ),

14. New Person ("Little Red",+),newperson ("Little Purple")};

16. Arrays.sort (a);

18. for (inti=0; i<a.length;i++)

20. System.out.print (A[i]);

22. System.out.print ("\ r \ n");

26. Arrays.sort (b);

28. for (inti=0; i<b.length;i++)

30. System.out.println (B[i]);

32. }

36. }

38. Custom Classes

40. class person {

44. Public String name;

48. Public intage;

52. Public Person (String name,intage) {

54. this. name=name;

56. this. age=age;

60. }

64. }

Program Run Result:

We find that string can call the Arrays.sort () function, and we customize the person class to make an error, looking at the wrong keyword comparable

Open String Source

By introducing the comparator comparable, we use the comparable interface below to implement the person using Arrays.sort () to sort the ascending order by age.

The comparable interface is able to sort the objects that implement its classes, using the CompareTo function primarily for sorting. The CompareTo function returns the int type, which returns -1,0,1, which corresponds to less than, equal to, greater than.

Change the code to:

Java code

2. Public class Mystring {

6. Public Static voidMain (string[] args) {

10. String []a={"Morning","Noon","Afternoon","Evening","Evening"};

14. Person[] b={ newperson ("small white",newperson ("Black",19 ),

16. New Person ("Little Red",+),newperson ("Little Purple")};

18. Arrays.sort (a);

20. for (inti=0; i<a.length;i++)

22. System.out.print (A[i]);

24. System.out.print ("\ r \ n");

28. Arrays.sort (b);

30. for (inti=0; i<b.length;i++)

32. System.out.println (B[i]);

34. }

38. }

40. Custom Classes

42. class Person implementscomparable<person>{

46. Public String name;

50. Public intage;

54. Public Person (String name,intage) {

56. this. name=name;

58. this. age=age;

62. }

64. Comparator comparison function

66. /**

68. * Returns 1 if the current object is less than the comparison object

70. * Returns 0 if the current object equals the comparison object

72. * Returns 1 if the current object is greater than the comparison object

74. */

76. @Override

78. Public intcompareTo (person O) {

80. Object is empty, throws a null pointer exception

82. if (o==null)

84. Throw New NullPointerException ();

86. if (this. age<o.age)

88. return-1;

90. if (this. age>o.age)

92. return 1;

94. return 0;

96. }

98. Overriding the ToString Method

100. @Override

102. Public String toString () {

104. return "person [name="+ name + ", age="+ Age + "]";

106. }

110. }

Operation Result:

To implement the comparer comparable interface for the custom person, you can call Arrays.sort () to sort.

there is another way to achieve Comparator interface.

Java code

2. Public class Mystring {

6. Public Static voidMain (string[] args) {

10. String []a={"Morning","Noon","Afternoon","Evening","Evening"};

14. Person[] b={ newperson ("small white","newPerson" ("small Black"),

16. New Person ("Little Red",+),newperson ("Little Purple")};

18. Arrays.sort (a);

20. for (inti=0; i<a.length;i++)

22. System.out.print (A[i]);

24. System.out.print ("\ r \ n");

28. Arrays.sort (b,newpersoncomparator ());

30. for (inti=0; i<b.length;i++)

32. System.out.println (B[i]);

34. }

38. }

40. Custom Classes

42. class person {

44. Public String name;

48. Public intage;

52. Public Person (String name,intage) {

54. this. name=name;

56. this. age=age;

60. }

62. @Override

64. Public String toString () {

66. return "person [name="+ name + ", age="+ Age + "]";

68. }

72. }

76. class Personcomparator implementscomparator<person>{

80. Comparator comparison function

82. /**

84. * Returns 1 if the current object is less than the comparison object

86. * Returns 0 if the current object equals the comparison object

88. * Returns 1 if the current object is greater than the comparison object

90. */

92. @Override

94. Public intCompare (person O1, person O2) {

96. Object is empty, throws a null pointer exception

98. if (o1==null| | o2==null)

100. Throw New NullPointerException ();

102. if (O1.age<o2.age)

104. return-1;

106. if (O1.age>o2.age)

108. return 1;

110. return 0;

112. }

116. }

Two. Cloning clone of an object

Copies a copy of an object, called the object's cloning technique. Cloning an object is a two-step move.

1. Implement cloneable Tag interface

Cloneable is a markup interface that does not have any methods defined by this interface. Just as a token to the virtual machine.

2. Overriding the Clone method of object

Java code

2. Custom class person implementation cloneable interface

4. class Person implementscloneable {

6. Public String name;

10. Public intage;

14. Public Person (String name,intage) {

16. this. name=name;

18. this. age=age;

22. }

24. Overriding the Clone method of object

26. @Override

28. protected Object Clone () throwsClonenotsupportedexception

30. {

32. return Super. Clone ();

34. }

38. }

Cloned calls:

Java code

1. Span>public static void main (string[] args) {

3. person temp= new person ( "Wang Nima" , + );

5. try {

6. person ok= (person) temp.clone (); //Convert the object class to person,

7. System.out.println (ok.name); Output Wang Nima

8. }  catch ( Clonenotsupportedexception e) {

9. E.printstacktrace ();

10. }

12. }

This can be done to clone an object, when we want to create a series of similar objects, you can consider the use of cloning technology can get better performance, than you create better.

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Java object comparer and cloning