equals方法和==的区别--用实例简单说明

首先我们创建一个类

public class People {

    private String name;
    private String address;

    public String getName() {
        return name;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public People() {
        super();
    }

    public People(String name, String address) {
        super();
        this.name = name;
        this.address = address;
    }

    @Override
    public String toString() {
        return "People [name=" + name + ", address=" + address + "]";
    }
}

该类没有重写hashcode和equals方法

下面我们进行比较

public static void main(String[] args) {

        People p1 = new People("a", "A");
        People p2 = new People("a", "A");
        People p3 = new People("b", "B");
        System.err.println(p1);
        System.err.println(p2);
        System.err.println(p3);
        System.err.println(p1.equals(p2));
        System.err.println(p1 == p2);
        System.err.println(p1.equals(p3));
        System.err.println(p1 == p3);

    }

结果为：

说明如果没有重写equals()方法，则equals和==比较的都是地址。每生成一个对象，虚拟机都会重新生成一个地址，因此比较结果都为false

我们加上hashcode和equals方法

public class People {

    private String name;
    private String address;

    public String getName() {
        return name;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public People() {
        super();
    }

    public People(String name, String address) {
        super();
        this.name = name;
        this.address = address;
    }

    @Override
    public String toString() {
        return "People [name=" + name + ", address=" + address + "]";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((address == null) ? 0 : address.hashCode());
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        People other = (People) obj;
        if (address == null) {
            if (other.address != null)
                return false;
        } else if (!address.equals(other.address))
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

}

再次运行实例，结果为：

说明如果重写equals()方法，则==比较的是地址，equals比较的是对象中的内容