操作符==总是用于对象引用比较，而String类.equals()方法用于内容比较被重写:

String s1 = new String("abc");
String s2 = new String("abc");
System.out.println(s1 == s2); // It prints false (reference comparison)
System.out.println(s1.equals(s2)); // It prints true (content comparison)

==操作符检查两个字符串是否完全相同的对象。

equals()方法将检查两个字符串是否具有相同的值。

功能:

public float simpleSimilarity(String u, String v) {
    String[] a = u.split(" ");
    String[] b = v.split(" ");

    long correct = 0;
    int minLen = Math.min(a.length, b.length);

    for (int i = 0; i < minLen; i++) {
        String aa = a[i];
        String bb = b[i];
        int minWordLength = Math.min(aa.length(), bb.length());

        for (int j = 0; j < minWordLength; j++) {
            if (aa.charAt(j) == bb.charAt(j)) {
                correct++;
            }
        }
    }

    return (float) (((double) correct) / Math.max(u.length(), v.length()));
}

测试:

String a = "This is the first string.";

String b = "this is not 1st string!";

// for exact string comparison, use .equals

boolean exact = a.equals(b);

// For similarity check, there are libraries for this
// Here I'll try a simple example I wrote

float similarity = simple_similarity(a,b);

我认为当你定义一个字符串时，你就定义了一个对象。所以你需要使用。equals()。当你使用基本数据类型时，你可以使用==，但对于String(和任何对象)，你必须使用.equals()。

操作符==总是用于对象引用比较，而String类.equals()方法用于内容比较被重写:

String s1 = new String("abc");
String s2 = new String("abc");
System.out.println(s1 == s2); // It prints false (reference comparison)
System.out.println(s1.equals(s2)); // It prints true (content comparison)

==执行引用相等性检查，2个对象(在本例中为字符串)是否引用内存中的同一对象。

equals()方法检查两个对象的内容或状态是否相同。

显然==更快，但如果你只是想知道2个字符串是否包含相同的文本，在许多情况下会(可能)给出错误的结果。

当然推荐使用equals()方法。

不要担心性能。使用String.equals()有以下几点值得鼓励:

Implementation of String.equals() first checks for reference equality (using ==), and if the 2 strings are the same by reference, no further calculation is performed! If the 2 string references are not the same, String.equals() will next check the lengths of the strings. This is also a fast operation because the String class stores the length of the string, no need to count the characters or code points. If the lengths differ, no further check is performed, we know they cannot be equal. Only if we got this far will the contents of the 2 strings be actually compared, and this will be a short-hand comparison: not all the characters will be compared, if we find a mismatching character (at the same position in the 2 strings), no further characters will be checked.

当一切都说了，做了，即使我们可以保证字符串是实习生，使用equals()方法仍然不是人们可能认为的开销，绝对是推荐的方式。如果您想要有效的引用检查，那么在语言规范和实现保证相同enum值将是相同对象(通过引用)的地方使用enum。