Arrays.sort(fruits, Fruit.FruitNameComparator) - Fruit static object FruitNameComparator

import java.util.Arrays;

public class ComparatorTest {
   
    public static void main(String[] args){
        Fruit fruit1 = new Fruit("banana",1);
        Fruit fruit2 = new Fruit("apple",2);
        Fruit fruit3 = new Fruit("orange",3);
        Fruit[] fruits = {fruit1, fruit2, fruit3};
        
        // we can write comparator based on properties
        Arrays.sort(fruits,Fruit.FruitNameComparator);
       
        for (Fruit fruit: fruits){
            System.out.println(fruit.getName());
        }
    }

}


import java.util.Comparator;

public class Fruit implements Comparable{
    public static final Comparator<Fruit> FruitNameComparator = new Comparator<Fruit>(){

        @Override
        public int compare(Fruit fruit1, Fruit fruit2) {
            // fruit1.getName() is String, String.compareTo
            // String, Integer, Double all have compareTo()
            return fruit1.getName().compareTo(fruit2.getName());
        }
       
       
    };
    public Fruit(String name, int quantity) {
        super();
        this.name = name;
        this.quantity = quantity;
    }
   
    String name;
    int quantity;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getQuantity() {
        return quantity;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
   
    // comparable means this object is comparable so it can compareTo other object
    @Override
    public int compareTo(Object compareFruit) {
        int compareFruitQuantity = ((Fruit)compareFruit).getQuantity();
        //ascending order
        return this.getQuantity() - compareFruitQuantity;
    }
   

}

OUTPUT
apple
banana
orange

Arrays.sort(Fruit) - Fruit needs to implement Comparable

Comparable is java.lang.Comparable
Comparator is java.util.Comparator

Comparable means this object is Comparable, it can compareTo other object
Comparator means tool can compare two objects, so it has method compare(object1, object2)

Comparable compare based on single property 
Comparator could compare based on multiple properties


import java.util.Arrays;

public class ComparableTest {
   
    public static void main(String[] args){
        Fruit fruit1 = new Fruit("banana",1);
        Fruit fruit2 = new Fruit("apple",2);
        Fruit fruit3 = new Fruit("orange",3);
        Fruit[] fruits = {fruit1,fruit2,fruit3};
       
        Arrays.sort(fruits);
       
        for (Fruit fruit:fruits){
            System.out.println(fruit.getName());
        }
    }

}

public class Fruit implements Comparable{
    public Fruit(String name, int quantity) {
        super();
        this.name = name;
        this.quantity = quantity;
    }
   
    String name;
    int quantity;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getQuantity() {
        return quantity;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
   
    // comparable means this object is comparable so it can compareTo other object
    @Override
    public int compareTo(Object compareFruit) {
        int compareFruitQuantity = ((Fruit)compareFruit).getQuantity();
        //ascending order
        return this.getQuantity() - compareFruitQuantity;
    }
   

}

OUTPUT
banana
apple
orange

Sort ArrayList using Collections.sort

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

public class SortArrayListTest {
   
    public static void main(String[] args){
        List list = new ArrayList();
        list.add("banana");
        list.add("apple");
        list.add("orange");
       
        Collections.sort(list);
       
        Iterator it = list.listIterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }

}

OUTPUT
apple
banana
orange

Sort Array using Arrays.sort

import java.util.Arrays;

public class SortArrayTest {
    public static void main(String[] args){
        String[] sa = {"banana","apple","orange"};
        Arrays.sort(sa);
       
        for (String s:sa){
            System.out.println(s);
        }
    }

}
OUTPUT
apple
banana
orange

Deep Copy

// deep copy, in clone() it creates a new object

public class DeepCopyTest {
   
    public static void main(String[] args) throws CloneNotSupportedException{
        Student student = new Student("Jet","Chinese"); // create student object
        Student student2 = student.clone(); // deep copy a new object student2
        System.out.println("student name="+student2.getName()+" subject="+student2.getSubject().getName());// print out this new object student2
        student.setName("Tom"); // change original object value
        student.getSubject().setName("English");
        System.out.println("student name="+student2.getName()+" subject="+student2.getSubject().getName()); // print out this new object value. it's changed.
               
    }

}


public class Student implements Cloneable{

    private String name;
    private Subject subject;
   
    public Student(String studentName, String subjectName) {
        this.name = studentName;
        this.subject = new Subject(subjectName);
    }

    @Override
    public Student clone() throws CloneNotSupportedException {
        Student student = new Student(name,subject.getName());
        return student ;
    }

    public String getName() {
        return this.name;
    }

    public Subject getSubject() {
        return this.subject;
    }

    public void setName(String studentName) {
        this.name = studentName;
    }

}
package deepcopy;

public class Subject {
    private String name;
   
    public Subject(String subjectName) {
        this.name = subjectName;
    }

    public String getName() {
        return name;
    }

    public void setName(String subjectName) {
            this.name = subjectName;
    }


}
OUTPUT


student name=Jet subject=Chinese
student name=Jet subject=Chinese

StringBuilder.insert - insert a string at position

public class InsertTest {
   public static void main(String[] args){
    StringBuilder sb = new StringBuilder("abcd");
    sb.insert(sb.indexOf("b"),"word");// insert word at position of b
   
    System.out.println(sb.toString());
   }

}
OUTPUT:
awordbcd

Shallow Copy

cloned object has own copy for primitive member but for object member, it will be shared with original object

http://www.jusfortechies.com/java/core-java/deepcopy_and_shallowcopy.php 

public class ShallowCopyTest {
   
    public static void main(String[] args) throws CloneNotSupportedException{
       
        Student stud = new Student("Jet","English");
        Student stud2 = (Student) stud.clone();
        System.out.println("student name="+stud2.getName()+" subject="+stud2.getSubject().getName());
        stud.setName("Tom");
        stud.getSubject().setName("Chinese");
        System.out.println("after original object is updated, cloned student name="+stud2.getName()+" subject="+stud2.getSubject().getName());
    }

}


public class Student implements Cloneable{

    private String name;
    private Subject subject;
   
    public Student(String studentName, String subjectName) {
        this.name = studentName;
        this.subject = new Subject(subjectName);
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    public String getName() {
        return this.name;
    }

    public Subject getSubject() {
        return this.subject;
    }

    public void setName(String studentName) {
        this.name = studentName;
    }

}