equals和==的區別？

若是是比較基本數據類型的只須要比較值就能夠

int a = 1;
		long b = 1l;
		double c = 1;
		System.out.println(a==b);
		System.out.println(b==c);
true
true

二者比較的都是地址值，

Student student1 = new Student();
Student student2 = new Student();
System.out.println(student1.equals(student2));
System.out.println(student1 == student2);

false
false

很容易理解，兩對象的地址值不一樣，因此都爲false。

再來看一段代碼

String s1 = "abc";
		String s2 = "abc";
		System.out.println(s1==s2);
		System.out.println(s1.equals(s2));
		
		System.out.println("------------");
		String s3 = "abc";
		String s4 = new String("abc");
		System.out.println(s3==s4);
		System.out.println(s3.equals(s4));
		
		System.out.println("---------------");
		String s5 = new String("abc");
		String s6 = new String("abc");
		System.out.println(s5==s6);
		System.out.println(s5.equals(s6));
true
true
------------
false
true
---------------
false
true

string類有點特殊，string s4 = "abc";,也至關於String s4 = new String("abc");代碼中s1==s2，是由於當定義string s2 = "abc"以前s1已經存在常量池中，因此s2直接指向了s1。這就使得s1==s2的返回值爲true。打開string類的equals方法，源碼是被重寫了的，

public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;

對象地址相同直接返回true,