Table of Contents

StringBuilder in Java with Examples

用於建立可修改字串，是一個非同步的操作，因為 String 類別建立了一個不可變的字串，所以使用 StringBuilder 類別來建立字串，用來取代 String 類別的替代方案，StringBuilder in Java 介紹常見的 appendCodePoint 、 codePoints 、 subSequence 等方法，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
       |                   +- stringbuilder
       |                       +- StringBuilderWithExamplesTest.java

單元測試

提供新增、反轉等操作 String 。

appendCodePoint

建立一個 StringBuilder ，增加 codePoint 。

	@Test
	public void appendCodePoint() {
		int expectedSize = 10;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		builder.appendCodePoint(32);
		builder.appendCodePoint(65);
		System.out.println(builder);
		assertEquals(expectedSize, builder.length());
	}

Java 147 A

codePoints

建立一個 StringBuilder ，增加字串，轉成 codePoint 。

	@Test
	public void codePoints() {
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		IntStream stream = builder.codePoints();
		List<Integer> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
	}

[74, 97, 118, 97, 32, 49, 52, 55]

codePointAt

StringBuilder Java 建立一個 StringBuilder ，增加字串後，取得指定索引的 codePoint 。

	@Test
	public void codePointAt() {
		int expected = 97;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.codePointAt(3);
		System.out.println(result);
		assertEquals(expected, result);
	}

codePointBefore

StringBuilder Java 建立一個 StringBuilder ，增加字串後，取得指定索引前的 codePoint 。

	@Test
	public void codePointBefore() {
		int expected = 118;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.codePointBefore(3);
		System.out.println(result);
		assertEquals(expected, result);
	}

codePointCount

Java StringBuilder 建立一個 StringBuilder ，增加字串，取得 codePoint 數量。

	@Test
	public void codePointCount() {
		int expected = 3;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.codePointCount(0, 3);
		System.out.println(result);
		assertEquals(expected, result);
	}

offsetByCodePoints

Java StringBuilder 建立一個 StringBuilder ，建立一個 StringBuilder ，增加字串後，取得指定索引偏移量的 codePoint 。

	@Test
	public void offsetByCodePoints() {
		int expected = 5;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.offsetByCodePoints(1, 4);
		System.out.println(result);
		assertEquals(expected, result);
	}

subSequence

Java StringBuilder 建立一個 StringBuilder ，增加字串後，取得指定索引區間的字串。

	@Test
	public void subSequence() {
		CharSequence expected = "Java";
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		CharSequence result = builder.subSequence(0, 4);
		System.out.println(result);
		assertEquals(expected, result);
	}

Java

reverse

Java StringBuilder 建立一個 StringBuilder ，增加字串後，取得反轉字串。

	@Test
	public void reverse() {
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147, ");
		builder.append("Spring boot 168");
		StringBuilder result = builder.reverse();
		System.out.println(result);
	}

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StringBuilderWithExamplesTest.java

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

package org.ruoxue.java_147.string.stringbuilder;

import static org.junit.Assert.*;

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

import org.junit.Test;

public class StringBuilderWithExamplesTest {

	@Test
	public void appendCodePoint() {
		int expectedSize = 10;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		builder.appendCodePoint(32);
		builder.appendCodePoint(65);
		System.out.println(builder);
		assertEquals(expectedSize, builder.length());
	}

	@Test
	public void codePoints() {
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		IntStream stream = builder.codePoints();
		List<Integer> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
	}

	@Test
	public void codePointAt() {
		int expected = 97;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.codePointAt(3);
		System.out.println(result);
		assertEquals(expected, result);
	}

	@Test
	public void codePointBefore() {
		int expected = 118;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.codePointBefore(3);
		System.out.println(result);
		assertEquals(expected, result);
	}

	@Test
	public void codePointCount() {
		int expected = 3;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.codePointCount(0, 3);
		System.out.println(result);
		assertEquals(expected, result);
	}

	@Test
	public void offsetByCodePoints() {
		int expected = 5;
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		int result = builder.offsetByCodePoints(1, 4);
		System.out.println(result);
		assertEquals(expected, result);
	}

	@Test
	public void subSequence() {
		CharSequence expected = "Java";
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147");
		CharSequence result = builder.subSequence(0, 4);
		System.out.println(result);
		assertEquals(expected, result);
	}

	@Test
	public void reverse() {
		StringBuilder builder = new StringBuilder();
		builder.append("Java 147, ");
		builder.append("Spring boot 168");
		StringBuilder result = builder.reverse();
		System.out.println(result);
	}

}