Table of Contents

Java StringJoiner Methods

用來簡化指定分割符號來拼接字串，並且可以選擇前綴、後綴符號，雖然使用 StringBuilder 在每個字串後附加分割符號，也能夠實現，但 StringJoiner 提供了一種無需撰寫太多程式碼，更加簡便的方式， StringJoiner Java Methods 本篇增加了範例，並透過單元測試來驗證產出結果。

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- string
       |                   +- stringjoiner
       |                       +- StringJoinerMethodsTest.java

單元測試

提供指定前綴、後綴及分隔符號等拼接字串。

add

建立一個 StringJoiner ，指定分隔符號，拼接字串。

	@Test
	public void add() {
		StringJoiner joiner = new StringJoiner(",");
		joiner.add("Java");
		joiner.add("Spring");
		joiner.add("JUnit");
		System.out.println(joiner);
		assertEquals("Java,Spring,JUnit", joiner.toString());
	}

Java,Spring,JUnit

prefixAndSuffix

建立一個 StringJoiner ，指定前綴、後綴及分隔符號，拼接字串。

	@Test
	public void prefixAndSuffix() {
		StringJoiner joiner = new StringJoiner(",", "[", "]");
		joiner.add("Java");
		joiner.add("Spring");
		joiner.add("JUnit");
		System.out.println(joiner);
		assertEquals("[Java,Spring,JUnit]", joiner.toString());
	}

[Java,Spring,JUnit]

merge

StringJoiner Methods in Java 建立兩個 StringJoiner ，指定前綴、後綴及分隔符號，使用 merge 拼接字串。

	@Test
	public void merge() {
		StringJoiner joiner = new StringJoiner(",", "[", "]");
		joiner.add("Java");
		joiner.add("Spring");
		StringJoiner joiner2 = new StringJoiner("-", "[", "]");
		joiner2.add("JUnit");
		joiner2.add("Assertj");
		joiner.merge(joiner2);
		System.out.println(joiner);
		assertEquals("[Java,Spring,JUnit-Assertj]", joiner.toString());
	}

[Java,Spring,JUnit-Assertj]

length

StringJoiner Methods in Java 建立一個 StringJoiner ，增加字串，取得長度。

	@Test
	public void length() {
		int expectedSize = 17;
		StringJoiner joiner = new StringJoiner(",");
		joiner.add("Java");
		joiner.add("Spring");
		joiner.add("JUnit");
		System.out.println(joiner.length());
		assertEquals(expectedSize, joiner.length());
	}

setEmptyValue

StringJoiner Methods in Java 建立一個 StringJoiner ，預設空值。

	@Test
	public void setEmptyValue() {
		StringJoiner joiner = new StringJoiner(",");
		joiner.setEmptyValue("default");
		System.out.println(joiner);
		assertEquals("default", joiner.toString());
	}

default

String_join

StringJoiner Methods Java 使用 String join ，指定分隔符號，拼接字串。

	@Test
	public void String_join() {
		String[] array = { "Java", "Spring", "JUnit" };
		String result = String.join(",", array);
		System.out.println(result);

Java,Spring,JUnit

Collectors_joining

StringJoiner Methods Java 使用 Collectors joining ，指定前綴、後綴及分隔符號，拼接字串。

	@Test
	public void Collectors_joining() {
		List<String> list = Arrays.asList("Java", "Spring", "JUnit");
		String result = list.stream().map(e -> e.toString()).collect(Collectors.joining(","));
		System.out.println(result);
		assertEquals("Java,Spring,JUnit", result);

		result = list.stream().map(e -> e.toString()).collect(Collectors.joining(",", "[", "]"));
		System.out.println(result);
		assertEquals("[Java,Spring,JUnit]", result);
	}

Java,Spring,JUnit
[Java,Spring,JUnit]

StringJoinerMethodsTest.java

StringJoiner Methods in Java 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.string.stringjoiner;

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.List;
import java.util.StringJoiner;
import java.util.stream.Collectors;

import org.junit.Test;

public class StringJoinerMethodsTest {

	@Test
	public void add() {
		StringJoiner joiner = new StringJoiner(",");
		joiner.add("Java");
		joiner.add("Spring");
		joiner.add("JUnit");
		System.out.println(joiner);
		assertEquals("Java,Spring,JUnit", joiner.toString());
	}

	@Test
	public void prefixAndSuffix() {
		StringJoiner joiner = new StringJoiner(",", "[", "]");
		joiner.add("Java");
		joiner.add("Spring");
		joiner.add("JUnit");
		System.out.println(joiner);
		assertEquals("[Java,Spring,JUnit]", joiner.toString());
	}

	@Test
	public void merge() {
		StringJoiner joiner = new StringJoiner(",", "[", "]");
		joiner.add("Java");
		joiner.add("Spring");
		StringJoiner joiner2 = new StringJoiner("-", "[", "]");
		joiner2.add("JUnit");
		joiner2.add("Assertj");
		joiner.merge(joiner2);
		System.out.println(joiner);
		assertEquals("[Java,Spring,JUnit-Assertj]", joiner.toString());
	}

	@Test
	public void length() {
		int expectedSize = 17;
		StringJoiner joiner = new StringJoiner(",");
		joiner.add("Java");
		joiner.add("Spring");
		joiner.add("JUnit");
		System.out.println(joiner.length());
		assertEquals(expectedSize, joiner.length());
	}

	@Test
	public void setEmptyValue() {
		StringJoiner joiner = new StringJoiner(",");
		joiner.setEmptyValue("default");
		System.out.println(joiner);
		assertEquals("default", joiner.toString());
	}

	@Test
	public void String_join() {
		String[] array = { "Java", "Spring", "JUnit" };
		String result = String.join(",", array);
		System.out.println(result);
		assertEquals("Java,Spring,JUnit", result);
	}

	@Test
	public void Collectors_joining() {
		List<String> list = Arrays.asList("Java", "Spring", "JUnit");
		String result = list.stream().map(e -> e.toString()).collect(Collectors.joining(","));
		System.out.println(result);
		assertEquals("Java,Spring,JUnit", result);

		result = list.stream().map(e -> e.toString()).collect(Collectors.joining(",", "[", "]"));
		System.out.println(result);
		assertEquals("[Java,Spring,JUnit]", result);
	}
}