"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:

2. public class Mystring {
   

4. 
   

6. public static void Main (string[] args) {
   

8. 
   

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

12. 
    

14. Person[] b={New Person ("small white", new Person ("black", 19),
    

16. New person ("Little Red", +), new person ("Little Violet", 20)};
    

18. Arrays.sort (a);
    

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

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

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

26. 
    

28. Arrays.sort (b);
    

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

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

34. }
    

36. 
    

38. }
    

40. Custom Classes
    

42. Class Person {
    

44. 
    

46. public String name;
    

48. 
    

50. public int age;
    

52. 
    

54. Public person (String Name,int age) {
    

56. This.name=name;
    

58. This.age=age;
    

60. 
    

62. }
    

64. 
    

66. }

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program run Result:
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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

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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:

2. public class Mystring {
   

4. 
   

6. public static void Main (string[] args) {
   

8. 
   

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

12. 
    

14. Person[] b={New Person ("small white", new Person ("black", 19),
    

16. New person ("Little Red", +), new person ("Little Violet", 20)};
    

18. Arrays.sort (a);
    

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

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

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

26. 
    

28. Arrays.sort (b);
    

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

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

34. }
    

36. 
    

38. }
    

40. Custom Classes
    

42. Class Person implements comparable<person>{
    

44. 
    

46. public String name;
    

48. 
    

50. public int age;
    

52. 
    

54. Public person (String Name,int age) {
    

56. This.name=name;
    

58. This.age=age;
    

60. 
    

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 int compareTo (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. }
     

108. 
     

110. }

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

There is another way to implement the comparator interface.

2. public class Mystring {
   

4. 
   

6. public static void Main (string[] args) {
   

8. 
   

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

12. 
    

14. Person[] b={New Person ("small white", new Person ("black", 19),
    

16. New person ("Little Red", +), new person ("Little Violet", 20)};
    

18. Arrays.sort (a);
    

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

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

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

26. 
    

28. Arrays.sort (B,new personcomparator ());
    

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

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

34. }
    

36. 
    

38. }
    

40. Custom Classes
    

42. Class Person {
    

44. public String name;
    

46. 
    

48. public int age;
    

50. 
    

52. Public person (String Name,int age) {
    

54. This.name=name;
    

56. This.age=age;
    

58. 
    

60. }
    

62. @Override
    

64. Public String toString () {
    

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

68. }
    

70. 
    

72. }
    

74. 
    

76. Class Personcomparator implements comparator<person>{
    

78. 
    

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 int Compare (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. }
     

114. 
     

116. }

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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

2. Custom class person implementation cloneable interface
   

4. Class Person implements Cloneable {
   

6. public String name;
   

8. 
   

10. public int age;
    

12. 
    

14. Public person (String Name,int age) {
    

16. This.name=name;
    

18. This.age=age;
    

20. 
    

22. }
    

24. Overriding the Clone method of object
    

26. @Override
    

28. Protected Object Clone () throws Clonenotsupportedexception
    

30. {
    

32. return Super.clone ();
    

34. }
    

36. 
    

38. }

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Cloned calls:

2. public static void Main (string[] args) {
   

4. 
   

6. Person Temp=new person ("Wang Nima", 18);
   

8. 
   

10. try {
    

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

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

16. } catch (Clonenotsupportedexception e) {
    

18. E.printstacktrace ();
    

20. }
    

22. 
    

24. }

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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 a better

"Java object comparer and cloning"