Java AbstractList equals()方法及示例

java.util.AbstractList 类的 equals() 方法用于比较指定对象和这个列表是否相等。当且仅当指定的对象也是一个列表，两个列表具有相同的大小，并且两个列表中所有相应的元素对都相等时，返回真。(如果(e1==null ? e2==null : e1.equals(e2))，两个元素e1和e2是相等的。)换句话说，如果两个列表以相同的顺序包含相同的元素，那么它们被定义为是相等的。

语法

public boolean equals(Object o)

参数： 该方法以对象o为参数，与该列表进行平等比较。

返回值： 如果指定的对象与这个列表相等，该方法返回真。

下面是说明 equals() 方法的例子。

例1 :

// Java program to demonstrate
// equals() method
// for String value
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            // Creating object of AbstractList<String>
            AbstractList<String>
                arrlist1 = new ArrayList<String>();
  
            // Populating arrlist1
            arrlist1.add("A");
            arrlist1.add("B");
            arrlist1.add("C");
            arrlist1.add("D");
            arrlist1.add("E");
  
            // print arrlist1
            System.out.println("First ArrayListlist : "
                               + arrlist1);
  
            // Creating another object of AbstractList<String>
            AbstractList<String>
                arrlist2 = new ArrayList<String>();
  
            // Populating arrlist2
            arrlist2.add("A");
            arrlist2.add("B");
            arrlist2.add("C");
            arrlist2.add("D");
            arrlist2.add("E");
  
            // print arrlist2
            System.out.println("Second ArrayList : "
                               + arrlist2);
  
            // comparing first ArrayList to another
            // using equals() method
            boolean value = arrlist1.equals(arrlist2);
  
            // print the value
            System.out.println("Are both list equal : "
                               + value);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

First ArrayListlist : [A, B, C, D, E]
Second ArrayList : [A, B, C, D, E]
Are both list equal : true

例2 :

// Java program to demonstrate
// equals() method
// for Integer value
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            // Creating object of AbstractList<Integer>
            AbstractList<Integer>
                arrlist1 = new ArrayList<Integer>();
  
            // Populating arrlist1
            arrlist1.add(10);
            arrlist1.add(20);
            arrlist1.add(30);
            arrlist1.add(40);
            arrlist1.add(50);
  
            // print arrlist1
            System.out.println("First ArrayListlist : "
                               + arrlist1);
  
            // Creating another object of AbstractList<Integer>
            AbstractList<Integer>
                arrlist2 = new ArrayList<Integer>();
  
            // Populating arrlist2
            arrlist2.add(10);
            arrlist2.add(20);
            arrlist2.add(30);
  
            // print arrlist2
            System.out.println("Second ArrayList : "
                               + arrlist2);
  
            // comparing first ArrayList to another
            // using equals() method
            boolean value = arrlist1.equals(arrlist2);
  
            // print the value
            System.out.println("Are both list equal : "
                               + value);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

First ArrayListlist : [10, 20, 30, 40, 50]
Second ArrayList : [10, 20, 30]
Are both list equal : false