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1. Use concat instead:

    String str = "test"; str = str.concat("test2"); str = str.concat("test3"); str = str.concat("test4"); str = str.concat("test5"); 

2. Use a single line of concatenation, which will create a single StringBuilder. Remember that each ; will create another StringBuilder:

    String str = "test" + "test2" + "test3" + "test4" + "test5"; 

3. Create a StringBuilder yourself, do the concatenation, and REUSE the StringBuilder. This has the best performance, specially when doing things in a loop.

    StringBuilder sb = new StringBuilder(512); for (int i = 0; i < 10000; i++) { sb.setLength(0); sb.append("test"); sb.append("test2"); sb.append("test3"); sb.append("test4"); sb.append("test5"); sb.append(i); String s = sb.toString(); } 

1. Use concat instead:

    String str = "test"; str = str.concat("test2"); str = str.concat("test3"); str = str.concat("test4"); str = str.concat("test5"); 

2. Use a single line of concatenation, which will create a single StringBuilder. Remember that each ; will create another StringBuilder. Note that in the concatenation of constant Strings below, the Java compiler will create a single String. However, if you add one or more String variables, then the StringBuilder will be created.

    String str = "test" + "test2" + "test3" + "test4" + "test5"; 

3. Create a StringBuilder yourself, do the concatenation, and REUSE the StringBuilder. This has the best performance, specially when doing things in a loop.

    StringBuilder sb = new StringBuilder(512); for (int i = 0; i < 10000; i++) { sb.setLength(0); sb.append("test"); sb.append("test2"); sb.append("test3"); sb.append("test4"); sb.append("test5"); sb.append(i); String s = sb.toString(); } 

So, from the code above, 4 different StringBuilders will be created. After the final String, all StringBuilders will be collected.

1. Use concat instead:

    String str = "test"; str = str.concat("test2"); str = str.concat("test3"); str = str.concat("test4"); str = str.concat("test5"); 

2. Use a single line of concatenation, which will create a single StringBuilder. Remember that each ; will create another StringBuilder:

    String str = "test" + "test2" + "test3" + "test4" + "test5"; 

3. Create a StringBuilder yourself, do the concatenation, and REUSE the StringBuilder. This has the best performance, specially when doing things in a loop.

 StringBuilder sb = new StringBuilder(512); for (;;) { sb.setLength(0); sb.append("test"); sb.append("test2"); sb.append("test3"); sb.append("test4"); sb.append("test5"); String s = sb.toString(); } 

Ps: sorry for some badly formatted output, but SO does not correctly shows my output for code.

1. Use concat instead:

    String str = "test"; str = str.concat("test2"); str = str.concat("test3"); str = str.concat("test4"); str = str.concat("test5"); 

2. Use a single line of concatenation, which will create a single StringBuilder. Remember that each ; will create another StringBuilder:

    String str = "test" + "test2" + "test3" + "test4" + "test5"; 

3. Create a StringBuilder yourself, do the concatenation, and REUSE the StringBuilder. This has the best performance, specially when doing things in a loop.

    StringBuilder sb = new StringBuilder(512); for (int i = 0; i < 10000; i++) { sb.setLength(0); sb.append("test"); sb.append("test2"); sb.append("test3"); sb.append("test4"); sb.append("test5"); sb.append(i); String s = sb.toString(); }