what operator to use when compare two strings in java code example

Example: compare two strings java

String string1 = "using equals method";String string2 = "using equals method";        String string3 = "using EQUALS method";String string4 = new String("using equals method"); assertThat(string1.equals(string2)).isTrue();assertThat(string1.equals(string4)).isTrue(); assertThat(string1.equals(null)).isFalse();assertThat(string1.equals(string3)).isFalse();