Comparative operation analysis of == and equals in java

Comparative analysis:

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==: Its function is to judge the two Are the addresses of the two objects equal? That is: determine whether two objects are the same object. (Basic data types compare values, and reference data types == compare memory addresses).

equals(): Its function is also to determine whether two objects are equal. But it generally has two usage cases, as follows:

Case 1: The class does not cover the equals() method. Then comparing two objects of this class through equals() is equivalent to comparing the two objects through ==.

Case 2: The class overrides the equals() method. Generally, we override the equals() method to ensure that the contents of the two objects are equal; if their contents are equal, true is returned (that is, the two objects are considered equal).

Code example:

public class test1 {
	public static void main(String[] args) {
		String a = new String("ab"); // a 为一个引用
		String b = new String("ab"); // b 为另一个引用,对象的内容一样
		String aa = "ab"; // 放在常量池中
		String bb = "ab"; // 从常量池中查找
		if (aa == bb) // true
		System.out.println("aa==bb");
		if (a == b) // false，非同一对象
		System.out.println("a==b");
		if (a.equals(b)) // true
		System.out.println("aEQb");
		if (42 == 42.0) // true
		System.out.println("true");
	}
}

The equals method in String has been overridden, because the equals method of object compares the memory address of the object, while the equals method of String compares the object. value. When creating an object of type String, the virtual machine searches the constant pool to see if there is an existing object with the same value as the one to be created, and if so, assigns it to the current reference. If not, re-create a String object in the constant pool.

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