java中String类型==判断及equals()判断

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1、java中String类型变量不同创建方式==判断情况如下：

import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class StringTest {
	private static final Logger logger = LoggerFactory.getLogger(StringTest.class);
	@Test
	public void testString() {
		
		String aString = "ja";
		String bString = "va";
		String cString = "java";
		String dString = aString + bString; // 反编译会发现是通过StringBuilder新建对象实现相加的
		logger.debug("dString == cString:{}", dString == cString); // false
		
		
		String eString = "java";
		String fString = "ja" + "va"; // 这是直接合并为"java",然后常量池中寻找相等对象
		logger.debug("eString == fString:{}", eString == fString); // true
	
		String gString = new String("java"); // new方法永远都新建对象
		logger.debug("eString == gString:{}", eString == gString); // false
		
	}
}

2、equals()方法String重写Object中的equals()方法，变为只判断值是否相等：

    public boolean equals(Object obj) { // Object中的equals()方法
        return (this == obj);
    }

    public boolean equals(Object anObject) { // String中重写的equals()方法
        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;
    }